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ELECTEO-PHYSIOLOGY 


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BY 

W.    BIEDERMANN 

PROFESSOR   OF   PHYSIOLOGY    IN  JENA 


TRANSLATED  BY  FRANCES  A.  WELBY 


WITH     ONE     HUNDRED    AND    THIRTY-SIX     FIGURES 


VOL.    I 


MACMILLAN   AND   CO.,  Ltd. 

NEW   YORK:    THE   MACMILLAN   CO. 

1896 

All  rights  reserved 


letifcatcb  in  fflctatttutje 


PEOF.    DR.    EWALD    HERING 


MY    VENERATED    MASTER 


Digitized  by  tine  Internet  Arciiive 

in  2010  with  funding  from 

Open  Knowledge  Commons 


http://www.archive.org/details/electrophysiolo01bied 


PKEFACE 

From  the  very  beginning  of  Experimental  Physiology,  the  mar- 
vellous action  of  electrical  currents  upon  excitable  animal  tissues, 
and  the  electrical  forces  which,  under  certain  conditions,  proceed 
from  these  tissues  themselves,  have  again  and  again  attracted  the 
attention  of  scientific  men,  and  have  given  rise  to  a  vast  number 
of  experiments,  which  at  the  present  day  are  still  being  prosecuted 
in  all  directions.  This  is  accounted  for  by  the  great  significance 
at  first  attributed  to  the  action  of  electrical  forces  in  the  living 
organism.  And  at  a  later  period,  when  these  anticipations  had 
not  been  fully  realised,  and  the  desired  goal  of  a  "  physical " 
explanation  of  muscular  contraction,  nerve  conductivity,  etc., 
seemed  farther  off  than  ever,  the  multitude  of  facts  meantime 
discovered,  together  with  the  exactness  of  the  methods  of  observa- 
tion,  and  the  conviction  that  perseverance  in  the  familiar  path 
must  eventually  lead  to  the  solution  of  some  at  least  of  the 
countless  problems  of  living  matter,  spurred  the  student  on  to 
renewed  endeavour.  Moreover,  there  was  a  growing  desire  to 
establish  the  many  and  successful  applications  of  electricity  in 
clinical,  medicine  on  a  firm  and  secure  basis,  and  to  found  an 
exact  science  of  electro-therapeutics.  Thus  it  has  come  about 
that  the  literature  of  Electro-Physiology,  in  a  wide  sense,  has 
swollen  to  a  bulk  that  practically  debars  any  student  who  is  not 
a  specialist  from  critical  acquaintance  with  it. 


viu  ELECTRO-PHYSIOLOGY 


Fifteen  years  have  elapsed  since  the  last  review  of  the  sub- 
ject by  Hermann,  in  his  Hcmdhuch  der  Physiologie — an  interval 
sufficient,  after  the  rapid  advances  in  this  department,  to  make 
a  new  account  desirable.  The  monographs  are  so  scattered,  and 
in  some  cases  so  little  accessible,  that  it  is  difficult  to  obtain 
a  synopsis  of  them.  I  have  worked  so  long  and  zealously  at 
this  particular  department,  and  have  in  preparation  for  my 
Lectures  acquired  a  familiarity  with  its  literature  (which  might 
otherwise  have  escaped  me),  so  great,  that  at  last  I  believe  myself 
justified  in  venturing  on  the  experiment  of  giving  a  comprehensive 
survey  of  Electro-Physiology — a  task  in  which  I  am  only  too 
well  aware  of  my  shortcomings.  Notwithstanding,  I  venture  to 
hope  that  I  have  rendered  a  service,  not  merely  to  many  of  my 
colleagues,  but  also  perhaps  to  a  portion  of  the  medical  public, 
since  I  have  aimed  at  a  connected  review  of  fundamental  facts, 
and  have  only  introduced  details  of  experimental  method,  and 
pure  theory,  where  they  were  indispensable  to  an  understanding 
of  the  subject.  The  chapter  on  Electrical  Fishes  in  particular  is 
commended  to  the  indulgence  of  my  fellow-workers  ;  it  could  only 
be  compiled  from  the  results  of  others,  as  I  have  no  first-hand 
experiences  to  draw  upon.  Those  who  know  its  widely-scattered 
literature  must  condone  the  defects  of  the  present  attempt,  in 
view  of  the  lack  of  any  other  summary.  As  an  excuse  for  the  size 
of  the  work  I  may  state  that  it  has  grown  out  of  my  lectures, 
and  could  only  thus  escape  a  certain  pedagogic  dryness.  In 
justification  of  the  sections  treating  of  Histology  and  General 
Physiology,  I  may  be  allowed  to  point  out  the  intimate  relations 
between  structure  and  function  in  muscle,  nerve,  and  electrical 
organs,  as  well  as,  on  the  other  hand,  the  necessity  of  premising 
the  discussion  of  more  special  questions,  with  the  general  con- 
ditions and  forms  of  manifestation  of  activity  in  irritable  tissues. 
Hence  it  seemed  to  me  not  merely  desirable,  but  imperative,  to 


PREFACE 


treat  these  relations  more  fundamentally  than  is  usual  in 
physiological  publications.  All  this  has  contributed  to  expand 
the  book,  perhaps  unduly,  beyond  its  natural  limits.  Again,  it 
may  be  objected  that  the  whole  survey  is  taken  from  one  definite 
standpoint,  so  that  individual  chapters  are  perhaps  treated  in  too 
one-sided  a  fashion.  But  I  frankly  confess  to  having  thought 
less  of  avoiding  a  subjective  tinge  by  the  elimination  of  every 
partisan  consideration,  than  of  showing  how  the  phenomena 
range  themselves  under  that  point  of  view  from  which  I  formerly 
learnt  to  judge  of  them  from  my  venerated  master,  Hering. 

In  dedicating  this  book  to  him  as  an  unworthy  token  of  my 
esteem  and  gratitude,  I  am  well  aware  that  I  am  only  giving 
back  what  I  formerly  received  from  him. 

Jena,  November  1894. 


CONTENTS 


IXTRODrCTIOX 


PAGE 
1 


CHAPTEE   I 

ORGAXISATIOX   AXD   STRUCTURE   OF   MUSCLE 

The  Muscles  of  Peotozoa  (Cell-muscles)  .  .  .  . 

The  Muscles  of  Metazoa  (Muscle-cells)  .  .  .  . 

BiBLIOGEAPHY  ....... 


3 

9 

52 


CHAPTEE   II 

CHAXGE   OF  FORM  IX  MUSCLE  DURIXG  ACTIVITY 

1.  DePEXDEXCE    OF    THE    PROCESS    OF    CONTEACTIOX   UPOX    THE    XaTURE    OF 

THE  Muscle    ........  57 

2.  Depexdexce  OF  Muscular  Coxteactiois""  upox  Strength  of  Excita- 

tion     .........  69 

3.  Effect    of    Loading    (Tension)    upon    Magnitude,    Duration   and 

Form  of  Muscular  Contraction    .  .  .  .  .76 

4.  Effect  of  Fatigue  upon  the  Process  of  Muscular  Contraction  .  S3 

5.  Effect  of  Temperature  on  Muscular  Contraction  .  .  .97 

6.  Effect  of  Chemical  Substances  upon  Muscular  Contraction        .  104 

Bibliography        ........  m 

7.  Summation  of  Stimuli  and  Tetanus      .....  113 

Bibliography        ........  143 

8.  Conductivity  of  Muscle   .......  144 

Bibliography        ........  172 


CONTENTS 


CHAPTER   III 

ELECTRICAL   EXCITATION   OF   MUSCLE 

PAGE 

The  Electrical  Excitation  of  Ukfibbillated  Pkotoplasm      .  .     299 

Summary  .........     313 

Bibliography         .  .  .  .  ...  .  .     318 

CHAPTER   IV 

ELECTROMOTIVE   ACTION   IN   MUSCLE 

1.  Current  of  Rest  in  Muscle        ......  321 

2.  The  Current  of  Action    .......  359 

3.  Positive  Variation  of  the  Muscle  Current   ....  432 

4.  Secondary  Electromotive  Action  in  Muscle  ....  442 

CHAPTER   V 

ELECTROMOTIVE   ACTION   OF   EPITHELIAL   AND   GLAND   CELLS 
Bibliography        ........     515 

INDEX   .  .'  .  .  .  .  .  .  .  .519 


INTEODUCTION 

Electeo-physiology,  as  set  forth  in  the  following  pages,  com- 
prises on  the  one  hand  the  theory  of  the  electrical  excitation  of 
excitable  tissues,  on  the  other  the  electromotive  reactions  which 
these  exhibit.  In  order  to  understand  the  subject,  an  adequate 
knowledge  of  the  phenomena  of  excitation,  and  in  particular  of 
the  effects  of  current  upon  living  matter,  is  essential,  and  must 
therefore  be  considered  in  the  first  instance.  While  in  Morpho- 
logy it  is  a  matter  of  course  that  any  inquiry  should  proceed 
from  simple  to  complex,  in  Physiology  experience  and  intuition 
alike  teach  us  that  the  converse  is  often  more  fertile  and  more 
expeditious.  This  is  due  in  part  to  the  nature  of  the  methods 
at  our  command,  in  part  to  fundamental  physiological  differences 
in  the  individual  elements.  What  is  morphologically  simple  is 
not  always  physiologically  intelligible  ;  in  a  sense  we  might  rather 
affirm  the  opposite.  If  it  be  true  that  every  function  of  the 
more  highly -developed  multicellular  organism  is  potentially 
nascent  in  the  relatively  undifferentiated  protoplasm  of  the 
amceba,  the  apparent  simplicity  of  the  latter  must  conceal  a 
complex  of  physiological  activities  not  to  be  compared  with  those 
cases  in  which  one  kind  of  cell  serves  only  one  single  function, 
as  a  muscle-cell  contraction,  a  gland-cell  secretion,  etc. 

Here  we  have  obviously  a  better  chance  of  acquiring  exact 
knowledge  of  the  inherent  qualities  of  the  physiological  function 
in  question  than  if  we  turn  to  primitive  organisms  whose  proto- 
plasm serves  indifferently  the  most  diverse  functions.  The  study 
of  glands  and  gland-cells  reveals  more  of  the  process  of  secretion 
than  the  investigation  of  the  same  process  in  unicellular  organisms, 
and  the  physiology  of  muscle  has  added  more  to  our  knowledge  of 
contraction  and  its  connected  processes  than  we  could  ever  have 


mTRODUCTION 


learned  from  microscopic  examination  of  lower  organisms.  It  is 
for  this  reason  that  muscle,  the  most  highly  differentiated  form 
of  contractile  tissue,  has  been  selected  as  the  point  of  departure  in 
the  following  attempt  at  a  comprehensive  survey  of  Electro- 
physiology. 


CHAPTEE  I 

OEGANISATIOX    AKD    STEUCTUEE    OF    MUSCLE 

Even"  at  a  low  grade  of  differentiation  there  is  a  wide  range  of 
Fibrillated  Structures  in  contractile  protoplasm,  and  the  great 
significance  of  this  organisation  for  the  contractile  process  and 
motor  phenomena  of  protoplasmic  substance  is  unmistakably 
attested  by  the  behaviour  of  ciliated  cells,  and  of  spermatozoa  in 
particular. 

Without  entirely  subscribing  to  the  theory  recently  brought 
forward  by  Ballowitz  (1)  and  others,  "  that  all  regular,  definitely 
canalised  contractions  of  contractile  substances  denote  the  presence 
of  regular,  parallel,  or  approximately  parallel  fibres "  (against 
which  there  is  much  counter-evidence),  it  is  nevertheless  remark- 
able that  a  fibrillated  structure  of  joroto'plasmj  is  mor-e  or  less  un- 
equivocally 'present  in  nearly  every  case  of  energetic,  and  especicdly 
of  rapid,  contractio7i.  This  is  expressed  most  clearly  in  the 
highest  differentiated  forms  of  contractile  animal  protoplasm,  i.e. 
Muscle-fibrils,  Muscle-cells,  and  Muscle-fibres. 

It  appears  to  be  of  fundamental  importance,  as  well  morpho- 
logically as  physiologically,  to  the  conception  of  "  muscle "  that 
structures  which,  in  virtue  of  organisation  and  function,  may 
properly  be  termed  muscular,  first  appear  as  single  and  isolated, 
or  fasciculated,  fibrils.  This  is  as  true  of  ontogenetic  as  of  phylo- 
genetic  development.  On  examining  the  latter,  we  encounter  the 
first  genuine  muscles  in  some  of  the  ciliated  Infusoria,  for  it  is  at 
least  doubtful  whether  the  delicate  and  swiftly  contracting  proto- 
plasmic threads  of  certain  fresh-water  Heliozoa  (Acanthocystiden), 
which  Engelmann  (2)  calls  "  myopodia,"  or  the  analogous  structure 
of  many  Eadiolaria,  the  "  myophrysken "  of  Haeckel,  are  true 
muscle-fibrils.      In  either  case  we  may  assume,  with  Engelmann, 


ELECTRO-PHYSIOLOGY 


that  these  structures  are  transitional  stages  between  pseudopodia 
and  muscle-fibrils  proper. 

If  we  examine  a  large  transparent  Vorticella  under  the  high 
power,  it  is  easy  to  detect  delicate,  converging  fibrils  just  below  the 
surface  ;  they  run  parallel  with  the  axis  of  the  body,  and  are  often 
finely  varicose.  Here  we  undoubtedly  have  a  differentiation 
product  of  the  ectoplasm  (Fig.  1),  whether — with  Blitschli  (3)— 
we  regard  these  fibrils  merely  as  a  longitudinal  series  of  cells 
within  the  otherwise  alveolar  protoplasm,  or  as  a  special  structural 
arrangement.  These  fibrils  {myonema)  converge  towards  the 
junction  of  the  stalk,  there,  in  most  cases,  uniting  into  a  cylindrical 

filament,  which  appears  fibrillated 
throughout  in  optical  transverse  section. 
Certain  of  the  Heterotricha  {Stentor, 
Siyirostomum)  and  Holotricha  {Holo- 
'pliyrct,  Prorodon,  O'pciliniden)  are  char- 
acterised by  a  much  more  pronounced 
development  of  muscular  fibrils.  Those 
of  Stentor,  isolated  by  Engelmann, 
were  as  much  as  1/i  in  diameter.  There 
were  even  indications  of  a  finer  struc- 
ture, i.e.  a  kind  of  transverse  stria tion 
(3,  p.  1000). 

Lieberklihn  recognised  the  fibrils 
of  Stentor  as  contractile  elements.  He 
observed  that  while  invariably  straight 
in  contracted  Stentors,  they  assume 
an  undulatory  appearance  as  soon 
as  the  infusorium  begins  to  lengthen,  becoming  elongated  during 
relaxation.  As  the  animal  grows  longer,  the  waves  become 
flatter.  The  fibrils  eventually  become  quite  straight  again,  and 
are  more  and  more  drawn  out  with  continued  extension.  In  the 
foot,  which  is  most  protracted,  they  lose  all  separate  identity ;  in 
the  rest  of  the  body  they  resemble  lines  of  excessive  fineness. 
"  If,  as  often  happens,  the  animals  shrink  slowly  together  during 
several  seconds,  instead  of  contracting  suddenly,  the  fibrils, 
instead  of  being  short,  thick,  and  straight  at  the  maximum  of 
contraction,  will  be  distinctly  wave -like,  and  not  perceptibly 
thicker  than  in  the  ordinary  extended  state  of  the  animal.  The 
waves  are  often  so  steep  and  short  that  the  fibres   come   into 


Fig.  1. — Carchesium  polypimim. 
(Biitschli.) 


I  ORGANISATION  AND  STRUCTURE  OF  MUSCLE  5 

lateral  contact.  The  cortical  layer  seems  at  first  sight  to  consist  of 
a  labyrinth  of  crumpled  fibres.  When,  after  slowly  retracting,  the 
animals  are  almost  globular,  there  is  still  a  possibility  of  con- 
traction. Every  fibril  suddenly  hecomes  short,  thick,  and  straight. 
Instead  of  the  labyrinth  of  little  waves  there  is  an  instantaneous 
reappearance  of  thick,  straight,  shining  longitudinal  stripes  lying 
parallel  with  one  another." 

Stentor  can  apparently  contract  spontaneously  without 
any  assignable  external  stimulus.  Engelmann  (2,  p.  447) 
found  on  applying  dilute  acetic  acid  (0"1  °/^),  HCl  (O'l  %), 
H.,SO^  (4  y^),  etc.,  that  single  fibrils  at  first  contracted 
frequently,  even  including  those  which  the  shrinking  of 
the  endoplasm  had  separated  from  the  pellicula.  Ether, 
chloroform,  and  the  electric  current  also  produce  a  sudden  con- 
traction of  the  muscular  layer  in  the  first  instance.  The  lower 
threshold  of  stimulation  differs  in  different  forms.  Stentor,  e.g., 
reacts  to  much  weaker  currents  than  Carchesium.  While  the 
current  is  passing,  the  protozoans  usually  remain  in  a  state  of  con- 
traction, but  when  it  is  weak  they  relax  completely  after  a  time, 
even  during  its  passage  (Stentor,  cf.  Verworn,  4,  p.  114). 

All  the  evidence,  therefore,  goes  to  prove  that  there  are  true 
excitable  and  contractile  fibrils  in  the  myoid  layer  (myonema)  of  the 
Infusoria  in  question,  and  that  it  is  the  rapid  shortening  of  these 
which  produces  the  body  twitches  of  Stentor  and  other  Infusors. 
Along  with  these,  however,  there  are  sloiver  contractions  (as 
already  stated),  which  indicate  that  the  remaining  'proto'plasm, 
which  is  comjjaratively  undifferentiated,  also  ])ossesses  contractility  in 
a  definite  direction.  In  these  contractions  the  muscle-fibrils  are 
bent  up  in  a  wavy  form,  and  are  therefore  relaxed.  The  endo- 
plasm cannot  here  play  an  active  part,  since,  although  contractile, 
it  streams  about  in  the  most  contrary  directions,  even  while  the 
animal  is  slowly  contracting.  The  fact  of  there  being  many 
highly  contractile  CUiata  {Hypotricha),  in  which,  nevertheless,  no 
fibrils  can  be  detected,  proves  that  the  differentiation  of  the 
latter  is  causally  connected  with  a  definite  kind  of  movement,  i.e. 
that  muscle- fibrils  subserve  only  i-apid  and  energetic  contractions. 
Of  this  the  most  salient  example  is  afforded  by  the  so-called 
"  stalk-muscle  "  of  Vorticella. 

As  we  have  seen,  the  fibrils  at  the  posterior  end  of  the  body 
of  Yorticella  converge  towards  the  neck  of  the  stalk.      In  Polyps 


ELECTRO-PHYSIOLOGY 


with  a  contractile  stalk  the  fibrils  do  not  end  here,  but  unite  to 
form  a  thread-like  organ,  which  enters  the  stalk,  and  usually  runs 
right  along  it.  This  filament  or  muscle,  almost  without  exception, 
runs  down  inside  the  sheath  of  the  stalk  in  a  sharp  spiral.  The 
sheath  is  a  cylindrical  tube  of  medium  diameter,  which  attaches 
itself  at  the  distal  end  to  some  foreign  body.  It  has  a  slender, 
elastic  wall  of  chitinous  composition.  The  interior  of  the  seem- 
ingly hollow  stalk  is  filled  with  a  homogeneous,  vitreous,  trans- 
parent mass  of  apparently  gelatinous  consistency.  In  Vorticella 
and  Carchesium  the  filaments  run  through  the  stalk  in  a  very 
elongated  spiral,  the  number  of  turns  varying  with  the  length  of 
the  pedicle.  According  to  Czermak  (5)  they  may  range  from 
0  to  12.  In  very  short -stalked  Vorticellte  there  may  be  only 
-^1  turn.  In  Zoothamnium  the  muscle  -  filaments  do  not  run 
peripherally  along  the  sheath  of  the  stalk  as  in  Vorticella  and 
Carchesium,  but  lie  close  to  the  axis,  surrounded  on  all  sides  by 
the  homogeneous  medullary  substance,  with  no  distinct  spiral. 

Since  the  filament  is  formed  by  the  junction  of  the  body- 
myonema,  we  may  presume  that  it  will  have  a  fibrillated  struc- 
ture. In  most  forms  the  fibrils  appear  to  lose  their  identity  in 
the  filament,  and  run  together  in  a  homogeneous  mass.  Yet  this 
can  be  in  appearance  only,  since  the  thick  muscle -threads  of 
certain  Zoothamnia  are  distinctly  fibrillated.  This  point  will  in 
all  probability  be  established  generally,  by  methods  similar  to 
those  which  Ballowitz  employed  to  discover  the  fibrillated  struc- 
ture of  the  flagellum  of  the  spermato-somata. 

The  contraction  phenomena  in  the  stalk  of  Vorticella  appear 
to  be  normally  sharp  and  sudden  ("  convulsive  ").  The  contrac- 
tion usually  affects  the  whole  stalk,  which  shrinks  into  a  low  and 
narrow-pitched  spiral  (helicoid),  the  turns  being  in  close  juxta- 
position. The  body  of  the  animal  usually  contracts  simultane- 
ously with  the  pedicle.  At  times  the  stalk  is  only  partially 
contracted,  and  both  the  upper  and  lower  halves  seem  able  to  shrink 
locally,  withou.t  implicating  the  remainder  (Czermak,  Klihne).  The 
unrolling  of  a  contracted  stalk  is  a  much  slower  process ;  it  also 
may  vary  in  direction,  beginning,  i.e.,  from  above  or  below,  and 
sometimes  remaining  incomplete  for  a  long  period. 

Czermak  {I.e.)  was  the  first  to  show  that  only  the  filaments  of 
the  stalk,  in  accordance  with  the  function  of  the  fibrils  of  the 
body-plasma,  are  the  seat  of  contractility ;  it  had  previously  been 


I  ORGANISATION  AND  STRUCTURE  OF  MUSCLE  7 

assumed  that  the  sheath  of  the  pedicle  was  the  contractile  organ. 
The  behaviour  of  VorticellEe,  whose  filaments  have  been  totally  or 
partially  destroyed,  affords  the  clearest  proof  in  favour  of  the  first 
view.  With  total  destruction  the  power  of  contraction  is  entirely 
abolished,  with  partial  destruction  the  loss  is  in  proportion  with 
the  injury. 

The  reaction  of  dead  stalks  is  interesting  in  this  connection. 
They  are  invariably  contracted  {rigor  mortis),  and  all  reagents 
that  kill  the  filaments  by  coagulation  (heat  included)  produce 
a  coiling  up  that  lasts  as  long  as  the  filaments  are  present. 
When  they  are  destroyed  by  decomposition,  or  by  reagents,  the 
stalk  lengthens  again.  These  experiments  show  that  the  elonga- 
tion depends  upon  the  elasticity  of  the  pedicular  sheath.  Engel- 
mann  {I.e.  p.  438  f.)  observed  in  Zootharanium  arbuscula  that  the 
fibrils  of  the  stalk-rnuscle,  which  in  this  case  are  quite  visible, 
become  short,  thick,  and  straight  at  the  moment  of  contraction. 
When  relaxation  begins,  they  lengthen  again  quickly,  so  that  if 
the  sheath  of  the  stalk  is  obstructed  by  any  accidental,  external 
obstacle,  and  thus  gets  slowly  longer,  the  fibrils  at  first  present 
a  very  sinuous  appearance.  The  stalk  -  filaments  of  Vorticella 
therefore  consist  undoubtedly  of  contractile  fibrils.  These  observa- 
tions (independently  of  other  facts  to  be  discussed  later)  seem 
to  disprove  the  conjecture  of  Klihne  (6)  that  it  is  not  the  filament 
itself,  but  the  sheath  of  the  filament — which  he  compares  with 
what  he  calls  the  "glia"  element  of  muscle -cells  in  higher 
animals — that  is  contractile,  the  filament  {i.e.  fibrils)  being  on  the 
contrary  an  elastic  tissue  that  produces  extension  in  conjunction 
with  the  sheath  of  the  pedicle. 

Assuming  the  fiament  of  the  stalk  to  be  the  contractile  ele- 
ment, it  is  easy  to  explain  the  spiral  coiling  and  uncoiling  of  the 
latter,  as  was  first  indicated  by  Czermak.  The  stalk  of  the  Con- 
tractilia  is  a  cylinder  with  a  thin,  elastic  wall,  to  the  inner 
surface  of  which  is  attached  a  contractile  filament  descending  in 
a  steep  spiral.  But  when  a  cylinder  contracts  along  a  spiral 
line  upon  its  surface,  it  also  becomes  spiral. 

Up  to  the  present  time  there  have  been  few  attempts  at 
artificial  excitation  of  the  stalk-muscle  of  Vorticella.  Klihne  (7) 
observed  that  Vorticella -colonies  contracted  suddenly  when 
tetanised  with  an  induction  current.  All  the  stalks  remain  con- 
tracted during  stimulation,  and  it  is  only  when  the  current  passes 


ELECTRO-PHYSIOLOGY 


for  a  prolonged  period  that  the  filaments  begin  to  expand  again 
during  tetanisation ;  the  animals  then  contract  only  slightly  from 
time  to  time,  although  if  the  current  is  strengthened,  they  can 
still  shrink  up  to  the  junction  with  the  bell.  Headless  stalks, 
when  isolated,  react  in  the  same  manner.  Chemical  stimuli 
(HCl  1  y^,  NH^)  also  cause  the  stalks  of  Vorticella  to  con- 
tract (Kiihne,  I.e.  p.  828).  With  a  dilute  solution  of  vera- 
trin  the  stalks  draw  together  slowly,  and  become  intensely 
rigid,  while  the  inner  muscular  filaments  grow  more  highly 
refractive,  and  therefore  much  more  visible.  A  very  dilute 
solution  of  strychnia  is  equally  fatal  to  Vorticella,  but  the  pheno- 
mena are  different.  The  animals  lose  their  excitability,  and 
remain  passively  extended,  although  there  is  a  continuous  ciliary 
movement.  In  this  state  the  strongest  induction  shocks,  as  well 
as  strong  solutions  of  curare,  fail  to  produce  any  movement 
(Kiihne,  I.e.) 

The  propagation  of  excitability  in  the  muscle  of  the  stalk 
should  also  be  more  exactly  studied.  There  can  be  no  doubt 
that  under  normal  conditions  spontaneous  excitation,  as  well  as 
contraction  caused  by  external  stimuli,  spreads  from  the  body  of 
the  vorticella.  The  excessive  rapidity  of  contraction  in  the  muscle- 
filament  makes  it  indeed  impossible  to  detect  where  the  process 
begins,  as  it  is  apparently  initiated  everywhere  at  the  same 
moment.  This  is  the  case  even  in  the  branched  colonies  of 
Zoothamnium,  or  Carchesium,  when  the  whole  community  is 
retracted  on  mechanically  exciting  one  individual.  In  Zootham- 
nium there  may  be  direct  conductivity  of  excitation,  since  every 
individual  is  a  conductor^,  to  the  rest  through  the  muscular  layer 
of  its  pedicle ;  but  in  Carchesium,  where  this  is  not  the  case,  the 
convulsion  communicated  from  one  contracting  individual  to  the 
next  appears  to  be  the  only  stimulus  (Verworn,  4).  In  order 
to  explain  the  phenomena  of  contraction,  not  merely  in  Vorti- 
cella, but  in  all  qther  myoid  Ciliata,  it  is  necessary  to  assume 
that  excitation  can  be  conveyed  from  every  point  of  the  body- 
plasma  to  the  muscle -fibrils,  which  are,  collectively,  in  juxta- 
position or  direct  connection  with  it ;  and  the  rate  at  which 
the  excitation  is  propagated  must  be  very  considerable,  under 
all  conditions  far  exceeding  that  of  the  Ehizopoda.  For  if 
a  spirostomum,  or  stentor,  which  from  their  elongated  form  are 
next    to    vorticella    the    best    suited    to    such    experiments,    be 


I  ORGANISATION  AND  STRUCTURE  OF  MUSCLE  9 

excited  locally,  at  one  end  only,  contraction  of  the  whole  body 
ensues  without  any  perceptible  latent  period ;  the  difference  of 
time,  which  doubtless  exists  in  contraction  of  the  anterior  and 
posterior  ends  of  the  animal,  being  quite  unnoticeable  (Verworn). 

The  Muscles  of  Metazoa 

In  Metazoa,  as  in  unicellular  animals,  the  typical  muscle 
makes  its  first  appearance  in  the  form  of  fibrils,  or  bundles  of 
fibrils,  in  the  protoplasm  of  certain  cells.  The  animal  kingdom 
exhibits  an  amazing  variety  in  regard  to  the  mass-disposition 
and  relative  arrangement  of  these  contractile  fibrils,  and  the 
formative  plasma  ("  sarcoplasm  "),  of  which  they  are  a  differentia- 
tion product. 

In  order  to  understand  the  structure  and  function  of  highly 
differentiated  nmscles,  it  is  as  important  to  consider  their  racial 
as  their  individual  development,  and  we  have  next  to  study 
in  detail  some  instructive  examples  of  the  first  of  these. 

The  simplest  form  of  muscle-cell  {myoplast  ^)  occurs  in  the  epi- 
thelial muscles  ("  neuro-muscular  cells  ")  of  the  lower  Coelenterata. 

In  Hydra,  e.g.,  the  ectoderm  consists  mainly  of  large,  blunt, 
cone-shaped,  epithelial  cells,  the  apices  of  which  are  directed 
inwards,  and  prolonged  into  one  or  more  processes  which  form 
dichotomously  branched  fibrils  bending  at  right  angles,  and  run- 
ning parallel  to  the  body  axis,  to  form  collectively  a  sub-epithelial, 
contractile  layer  ("  muscle  lamella  ").  Accordingly  in  transverse 
section  there  is  a  small  zone  between  the  ectoderm  and  endoderm, 
in  which  the  bisected  fibrils  stand  out  as  a  series  of  strongly 
refracting  points. 

In  this  case,  therefore,  the  cell-bodies  help  to  bound  the 
body-surface,  and,  like  the  protoplasm  of  Ciliata,  serve  to  establish 
relations  with  the  external  world,  since  they  are  able  to  receive 
impressions  from  without,  i.e.  are  excitable.  In  both  cases  the 
excitation  is  conveyed  through  the  protoplasm  of  the  cell  (sarco- 
plasm) to  the  contractile  fibrils,  and  must  be  able  to  spread  over 
large  tracts  of  the  body  by  conduction  from  cell  to  cell  (if  nerves 
are   really  wanting).      The  large,  vacuolated,  endoderm  cells   of 

^  In  the  ciliated  Infusoria  described  above,  which  must  be  regarded  as  inde- 
pendent cell-individuals,  it  is,  in  the  same  connection,  legitimate  to  speak  of  "  cell- 
muscles." 


10  ELECTRO-PHYSIOLOGY 


Hydra,  furnished  with  a  flagellum,  also  possess  basal  muscular 
fibrils.  A  similar  but  more  complicated  arrangement  exists  in 
the  Actinia.  We  are  still  in  every  case  dealing  with  muscles  of 
epithelial  origin,  e'pithelial  muscle- cells,  which  take  part  in  the 
external  or  internal  limitation  of  the  body-surface,  or  lie  deep 
down — their  epithelial  origin  being  always,  however,  unmistakable. 
In  the  simplest  case,  a  transverse  section  through  the  endoderm 
shows,  as  in  Hydra,  a  single  row  of  shining  granules,  lying  under 
a  single  layer  of  cylindrical,  epithelial  cells,  which  it  divides  from 
the  mesenchyme  (Fig.  2,  a). 

Here  again,  as  we  learn  from  isolated  preparations,  we  have 
a  cross-section  of  muscle-fibrils  (bundles 
/'//i  f/'^'^//       ^^  fibrils?)  which  must  be  regarded  as 
" '^'    '"         '  a    differentiation   product   of    the  epi- 

thelial cells.  The  cell-bodies  are  cubical, 
cylindrical,  or  filiform,  according  to 
the  state  of  contraction  of  the  body- 
wall  ;  they  carry  cilia,  or  a  solitary 
flagellum,  at  their  free  ends,  while 
muscle-fibrils  are  differentiated  off  at 
the  base,  which  is  somewhat  broader 
(Fig.  2,  h).  From  this  primitive  form 
it  is  easy  to  derive  what  Hertwig  (9) 

Fig.  2.— a,  Transverse  section  through    Calls       "  intra -epithelial"       mUSClcS,      in 

S!s::S;:;^S^«:Up:S  which    the   spindle-shaped    cell-bodies 


Y-rK'^t^i' 


d 


lar  to  the  long  axis  of  the  basal  are  Only  iuterspcrscd  between  the  epi- 

fibrils  ;    b,   epithelial   muscle  -  cell     ,iTin  iji  ,• 

(isolated)  of  Actinia.  (Hertwig.)  thchal  cclls  proper,  and  take  no  part  m 
bounding  the  upper  surface.  The  "  suh- 
eioithelial  "  muscles  are  directly  connected  with  these  forms  ;  they 
consist  of  long  fine  bands  (bundles  of  fibrils),  which  only  retain 
a  thin  sheet  of  formative  plasma  on  the  side  nearest  to  the 
epithelium. 

There  can  be  no  doubt  that  the  nucleated  mass  of  protoplasm 
here  corresponds  with  the  body  of  a  genuine  epithelial  muscle-cell. 
There  is  merely  a  structural  difference  between  the  last-named 
muscles  and  those  bundles  of  muscle-fibrils  which  are  completely 
surrounded  by  mesenchyme,  and  are  derived  from  a  corresponding 
number  of  myoblasts. 

The  individual  elements  in  this  case  also  are  fibres  (fibrils), 
with  plasma  and  nucleus ;  but  instead  of  lying  in  single  juxta- 


I  ORGANISATION  AND  STRUCTURE  OF  MUSCLE  11 

position,  they  unite  into  groups,  the  periphery  of  which  is  formed 
of  the  contractile  fibrils,  while  the  axis  contains  the  corresponding 
nuclei  and  protoplasm. 

Between  this  arrangement  and  the  original  superficial  dis- 
position of  the  muscle-fibrils  there  are  numerous  transitional 
stages,  produced  by  involution  of  the  muscular  lamella,  which 
obviously  tends  to  increase  the  mass  of  the  muscle  with  stationary 
body-superficies.  As  long  as  the  folding  of  the  muscle-lamella  is 
not  excessive,  the  irregularities  which  it  produces  towards  the 
free  surface  are  equalised  by  the  varying  lengths  of  the  epithelial 
cells.  The  supporting  mesenchyme  also  presses  from  ^ 
within  into  every  fold.      The  involution  varies  con-     .  I 

siderably  in  degree.      Sometimes  "  muscle-plates "  are  -  -j 

produced   which    stand   perpendicular    to    the    body-  1 

surface  in  close  juxtaposition,  like  the  leaves  of  a 
book  (Fig.  3).  Each  leaf  consists  of  a  thin  support- 
ing lamella  of  mesenchyme,  set  on  both  sides  with  > 
muscle-cells.  It  is  easy  to  see  how  by  such  a  '  jj 
process  of  involution  and  segregation,  carried  one  step  If 
farther,  the  cylindrical  fasciculi  of  muscles,  entirely  | 
surrounded  by  mesenchyme,  may  be  developed.                   ' '     '  7 

In  Medusa  we  meet   with  conditions  similar  to     ,^ J 

those  exhibited  by  Actinia.  The  muscle-fibrils,  which  fig.  3.— Trans- 
are  often  transversely  striated,  everywhere  exhibit  a     ^^^^  section 

«'  <^  oftliemuscles 

basal   differentiation    of    ectodermal,    epithelial    cells,     of  the  tociy- 

i-i  •  •  j_      T  1    1.T        ^       1  wall   of  Ceri- 

which  again  serve  m  many  cases  to  bound  the  body-     anthus  mem. 

surface.  hranaceus. 

A  structure  and  development  of  muscle,  similar  in 
many  respects  to  that  already  described  in  Cnidaria,  exists  conspicu- 
ously among  many  Worms  {Annulata),  where  the  epithelial,  or  at 
least  epithelioid,  character  of  the  muscle  is  still  immediately  recognis- 
able in  the  simplest  cases.  Here  the  longitudinal  muscle-fibres 
often  consist  of  mononuclear,  elongated  cells,  arranged  like  a  single- 
layered  epithelium.  Each  muscle-cell — isolated,  or  in  transverse 
section — shows  two  distinctly  separate  substances,  an  internal 
plasmatic  portion,  and  an  external  contractile  substance,  which 
again  is  constructed  of  countless  smooth  fibrils,  running  parallel 
with  the  long  axis  of  the  cell,  and,  as  seen  in  cross-section,  arranged 
in  laminse  lying  close  together,  so  that  the  contractile  layer 
exhibits  a  delicate  radial  striation.      Each  single  stripe  corresponds 


12 


ELECTRO-PHYSIOLOGY 


with  a  row  of  fibrils  lying  one  behind  the  other — dotted  in  trans- 
verse section  (Fig.  4,  B). 

The  relative  disposition  of  the  contractile  layer  and  formative 
plasma  (sarcoplasm)  varies  considerably  in  different  muscles  of 
worms.  In  the  simplest  case  each  muscle  is  represented  by  an 
even  lamina,  capped  by  the  nucleated  protoplasm  (Fig.  4,  B). 
It  is  evident  that  this  arrangement,  in  which  the  longitudinal 
muscular  fibrils  collectively  form  a  cylindrical  surface,  underlying 
the  hypodermis,  corresponds  with  the  smooth,  simple,  non-voluted 
muscular  lamella  of  many  Cnidaria.  In  both  cases  increase  of 
mass  in  the  contractile  substance  leads  to  a  formation  of  folds, 
which  in  Nematode  muscles  may  be  detected  in  each  single  cell. 
The  fibrillar  layer,  at  first  a  level  surface,  curves  into  a  hollow 
groove,  opening  into  the  coelom,  and  filled  with  formative  plasma. 


Fig.  i.—A,  BranchioMella  parasitica  ;  transverse  section  through  the  muscles  of  the  body-wall. 
a,  coelomyoicl ;  h,  holomyoid  muscle-cells.  B,  Section  through  a  platymyoid  muscle-cell  of 
Ascaris  lumhricoides.    (Rhode.) 

Ehode  (8),  e.g.,  finds  in  the  longitudinal  muscle-layer  of  Branchio- 
bdella  parasitica,  every  conceivable  form  of  transition  between  the 
"platymyoid"  type  of  muscle-cells  described  above,  in  which  the 
fibrillated  contractile  stratum  forms  an  even  lamina,  and  the 
"  coelomyoicl "  type,  where  the  fibrillar  layer  has  become  grooved 
(Fig.  4,  A,  a). 

And,  again,  there  is  but  a  step  from  these  to  the  closed  tubular 
muscle-cells,  in  which  the  plasma  forms  an  axial  filament  sheathed 
on  all  sides  by  the  contractile  fibres. 

The  longitudinal  fibres  of  the  sheath  of  the  cutaneous  muscle 
of  Ascaris  are  among  the  most  interesting  of  the  coelomyoid 
muscle-cells.  Here  the  sarcoplasm  is  already  walled  in  by  the 
contractile  substance  at  the  ends  of  many  of  the  muscle-cells, 
while  in  the  centre  the  nucleated  plasma  (surrounded  by  a 
sarcolemma)  bulges  out  like  a  hernial  sac,  and  is  often  of  gigantic 


ORGANISATION  AND  STRUCTURE  OF  MUSCLE 


13 


proportions  in  comparison  with   the    fibrillar    stratum   (Fig.    5, 
A,  B).      A  transverse  section  through  the  centre  of  such  a  cell 


Fig.  5. — A,  Section  through  part  of  the  muscular  layer  of 
Ascaris  himbricoides ;  a.,  vesicular  swellings  of  sarco- 
plasm  ;  |8,  contractile  substance  ;  y,  cell-nucleus.  (R. 
Leukart.)  B,  Isolated  muscle-cells  of  Ascaris,  from  the 
Bel.    (Hertwig.) 

shows  the  contractile  substance  in  a  horse-shoe 
figure,  with  the  sarcoplasm  rising  within  it ;  near 
the  ends  of  the  fibres  only  a  ring  of  contractile 
substance,  enclosing  a  cleft  filled  with  proto- 
plasm, is  exhibited.  In  many  cases  the  similarity 
of  arrangement,  in  transverse  section,  of  the 
fibrils  of  the  longitudinal  muscular  layer  of 
worms,  and  the  involuted  muscle  -  lamella  of 
certain  cnidarians,  is  very  striking. 

The  muscle-cells  of  most  other  worms  agree 
in  their  finer  structure  with  the  forms  described, 
being  either  of  a  flat,  a  hollow,  or  more  frequently 
a  tubular  type.  The  only  differences  are  in 
the  size  and  arrangement  of  the  separate 
elements,  and  also  in  the  comparative  develop- 
ment of  volume  of  the  sarcoplasm  and  con- 
tractile substance.  The  fibrillated  structure  of  the  contractile 
tissue  is  not  always  easy  to  distinguish,  but — cf.  Ehode  (I.e.)  on 
the   musculature    of   Chsetopoda — appears    to   be  very  generally 


14 


ELECTRO-PHYSIOLOGY 


distributed.  The  several  primitive  fibrils  are  rarely  detached 
from  the  formative  plasma  of  the  muscle-cell  as  a  single  layer, 
but  are  usually  clustered  together,  and  arranged  in  strata,  which 
gives  the  appearance  of  radial  striation  above  alluded  to,  in 
transverse  sections  of  the  contractile  layer. 

While  the  elaborate  structure  of  single  muscle -cells  in 
Annulata  undergoes  no  appreciable  change  as  development 
progresses,  there  is  on  the  other  hand  a  marked 
variety  in  regard  to  arrangement  of  the  muscle 
elements  into  filaments  and  bundles.  The  principle 
of  surface  growth  by  involution  is  still  paramount, 
and  just  as  in  single  muscle-cells  the  flat,  fibrillated 
lamina  curves  round  to  make  room  for  greater 
mass -development  of  the  contractile  substance, 
the  same  process  is  repeated  in  the  grouping 
together  of  a  number  of  muscle-cells  in  the  lonoi- 
tudinal  muscular  layer  of  many  Annulata. 

In  other  Lumbricidge  the  arrangement  of 
muscle-cells  inside  a  "  case "  is  still  more  regular, 
since  they  surround  the  central  hollow  in  a  single 
layer,  which  gives  a  feathered  appearance  to  the 
transverse  section.  The  axis,  which  corresponds 
to  the  shaft  of  the  feather,  is  bordered  on  either 
side  by  the  oblique  sections  of  the  myoblasts,  which 
cover  the  converging  sides  of  each  pair  of  cases 
(Fig.  6).  In  contrast  with  those,  the  longitudinal 
muscle-fibres  of  Lumbricus  olidus  and  many 
Oligochetse  lie  in  a  mass  of  irregular  layers,  or 
little     groups     divided    by    septa     of     connective 

The  original 

muscles 

IS  tnus   no  ionger  aiscmct  m  tne  arrangement  of 

the 

structure  of  the  single  cells  is  otherwise  perfectly  conformable. 
A  contractile,  fibrillated,  cortical  layer  can  always  be  distinguished 
from  a  medullary  substance  (sarcoplasm),  which  it  wholly  or 
partially  encloses.  The  usually  solitary  nucleus  either  lies  to 
one  side  on  the  margin  or  surface  of  the  separate  fibres,  or  {e.g. 
in  Hirudinai)  within  the  central  protoplasmic  hollow.      In  many 


Pig.  6.— Transverse  ^issuc,  as  also  occurs  in  Hirudiuse. 

section  of   body-  .  n       i  i  •        t 

muscles  of  £wm-  epithelial    character   of   the    longitudinal 

bricus     maxinm^s.    •       ^j  ^^    ^  distiuct    in    the 

(Rhode.)  f 

the    individual   elements   in  such   cases ;    but 


Annulata,  as  in  Cnidaria,  the  involution  of  the  muscular  lamella 


ORGANISATION  AND  STRUCTURE  OF  MUSCLE 


is  excessively  developed,  and  produces  very  complicated  figures  in 
transverse  section.  Certain  Polychoetce,  in  particular,  exhibit  an 
extraordinarily  complex  arrangement  of  the  flat  band-like  muscle- 
cells,  which  are  individually  of  very  insignificant  proportions. 
The  cross-section  of  the  longitudinal  muscle-layer  not  infrequently 
acquires  a  characteristic  appearance. 

The  muscle-fibres  of  Cephalopoda  should  be  mentioned  as 
affording  in  many  respects  a  remarkable  instance  of  muscle-cells 
in  Invertebrates.  Their  peculiar  structure  has  recently  been 
investigated  by  Ballo- 


mmmm 


witz  (10). 

With  both  the 
high  and  low  power 
a  system  of  parallel 
lines  appears,  running 
obliquely  in  opposite 
directions,  and  seem- 
ing with  the  medium 
power  to  cross  directly 
over  one  another 
(Fig.  8).  The  ex- 
amination of  partially 
destroyed  muscle-cells 
shows  this  to  be  the 
optical  expression  of 
fibres  which  "  run  in 
a  continuous  spiral  in 
the  cortex  round  the  pig 
medullary  substance." 
The  steepness  of  the  spirals  varies  considerably  with  the  state  of 
contraction.  In  very  flat  muscle-cells  both  systems  of  striation 
appear  to  lie  almost  in  the  same  plane,  giving  an  appearance  of 
"double  oblique  striation,"  first  described  by  Schwalbe  (11)  for 
several  of  the  Invertebrates.  Schwalbe  explained  these  figures 
on  the  assumption  that  the  fibres  were  composed  of  rhombic 
"  sarcous  elements,"  while  Engelmann  (12)  at  a  later  period 
pointed  out  their  fibrillated  structure,  and  maintained  "  that 
every  fibre  with  double  oblique  striation  consists  of  two  systems 
of  fibrils  in  concentric  layers  parallel  to  the  surface  of  the  fibre, 
which  describe  a  spiral  in   opposite  directions   round   its   axis." 


-Transverse  section  of  body-muscles  of  Protula  -protensa. 
(Rhode.) 


16 


ELECTRO-PHYSIOLOGY 


We  furtlier  learn  with  regard  to  the  finer  structure  of  these 
muscle-cells,  from  transverse  sections,  that  the  XDroportion  between 
cortical  and  medullary  substance  varies  enormously  in  different 
elements  of  the  same  section.  "  The  cortex  may  be  small,  and 
enclose  a  larger  axial  hollow,  while  other  adjacent  sections  show 
a  broad  ring,  with  a  narrow  central  lumen  "  (different  states  of 
contraction).  In  nearly  all  muscle-cells,  especially  in  stained 
preparations  of  the  cross-sections,  it  is  possible  to  detect  a  radial 
striation  of  the  cortical  substance,  similar  in  all  respects  to  that 

described  above  in  the 
muscle -cells  of  Nematoda 
and  Annulata,  and  therefore 
to  be  interpreted  as  the  ex- 
pression of  a  fibrillated 
structure  (Fig.  9). 

There  is  a  regular  alter- 
nation of  dark  and  light 
striation,  and  it  is  easy  to  see 
that  the  dark  lines  correspond 
with  cross  -  sections  of  the 
spiral  fibres,  which  must  ac- 
cordingly be  flat  and  band- 
like, while  the  colourless 
radii  represent  an  intermedi- 
ate substance.  This  appears, 
inter  alia,  from  the  fact  that 
in  focussing  a  thicker  cross- 
section  of  a  muscle-fibre  "  the 
dark  lines  all  run  out  simul- 


^ 
t 


b 

^ 

0' 

1      r 

i 

^l  ■■ 

\ 

[ 

« 

1 

i     1 

I     ' 

^'y^  ^  '■v 


J 


Pig.  8. — Segment  of  isolated  muscle-cell  from  Sc2nola 
Rondeletii  under  (a)  high,  (h)  medium,  and  (c)  low 
power.    (Ballowitz.) 


taneously  in  the  same  direction  like  the  spokes  of  a  wheel,"  when 
the  tube  of  the  microscope  is  gradually  lowered.  The  spiral  fibres 
of  the  cortex  therefore  form  flat  bands,  which  run  in  a  single  layer 
throughout  its  entire  thickness.  These  spiral  lamellae  obviously 
correspond  with  the  radial  "  fibrillar  laminse "  of  the  muscles 
described  above,  and  exhibit  a  further  differentiation  into  delicate 
homogeneous  fibrils,  the  proper  elements  of  the  cortex.  The 
reaction  of  these  muscle-fibres  to  gold  chloride  is  of  great  interest, 
especially  in  view  of  certain  facts  which  we  shall  discuss  later. 
Only  the  axial  sarcoplasm  is  stained  under  some  conditions,  together 
with  the  interstitial  substance  that  separates  the  spirals  of  the 


I  ORGANISATION  AND  STRUCTURE  OF  MUSCLE  17 

lamella,  and  does  not  stain  with  any  other  reagent.  The  lamella 
itself  remains  colourless.  This,  as  will  presently  appear,  arises  from 
a  reaction  common  to  all  muscles — on  the  one  hand,  of  the  plas- 
matic ground- substance,  on  the  other,  of  the  contractile  fibrils — 
which  thus  affords  an  invaluable  means  of  studying  the  distribu- 
tion of  the  two  within  one  fibre.  From  this  reaction  we  may 
conclude  that  the  interfibrillar  substance  (which  of  course  forms  a 
a  spiral  lamella)  is  identical  with  the  axial  sarcoplasm,  so  that  the 
cortical  substance  in  other  cases   also  should  contain  formative 

plasma   in  addition  to    the    con-     ^^— 

tractile'  fibrils,  —  as    is   directly     ^        ; 
proved     by    the   radial    striation     ;    C  ._^_, 
of    the    cross  -  sections.        There     ' 
is,  however,    a     deplorable    lack 
of     any     systematised     compara-    '  ^. 
tive    observations    on     the    finer 
structure  of  invertebrate  muscle    I 
according  to  modern  methods. 
Knoll    (13),  writing   on    the 

relative     scarcity     and      abund-  "'^Ij 

.  ,7' 

ance    of   protoplasm    in    muscle-    i 

fibres,     communicated     numerous    ; 

data,  which,    however,   bear    less    j 

on    the    finer    structure    of    the     1  V 

cortical    substance    than    on    the     \  _  •; 

proportion     between     sarcoplasm - --"- 

and  contractile  substance  in  Fig.  9.— Transverse  section  of  muscle-cell  from 
,1  1  f.  I    T        I  1      the  mantle  of  Eledone  moschata.   (Ballowitz.) 

the    muscles    01     vertebrate    and 

invertebrate  animals.  From  these,  as  well  as  from  earlier  re- 
searches (H.  Fol,  14),  it  is  evident  that  the  muscle-cells  of  Lamelli- 
branchs  and  Gasteropods  have  in  many  cases  the  same  structure 
as  those  of  Cephalopoda.  The  appearance  of  double  oblique 
(in  many  cases  also  of  transverse)  striation  in  the  muscle-cells  of 
the  adductor  muscle  of  the  Lamellibranchs  is  very  interesting. 
Fol,  previous  to  Ballowitz,  had  established  an  analogous  theory 
of  structural  relations,  since  he  described  the  contractile  sheath 
of  the  spindle-cells  as  consisting  of  fibrils  running  spirally  round 
the  plasmatic  axis.  Like  Ballowitz,  he  referred  the  figure  of 
quadratic  or  rhombic  arese,  first  described  by  Schwalbe,  simply  to 
the  crossing  of  the  two  halves  of  the  spiral  windings,  running 

c 


18  ELECTEO-PHYSIOLOGY 


above  and  below  the  axis.  Ehocle  {I.e.)  noticed  the  same  appear- 
ance in  the  bi-obliquely  striated  muscle -cells  of  many  worms 
{Arenicola,  NepMhys).  The  bisected  adductor  muscle  of  Molluscs 
often  shows,  even  to  the  naked  eye,  a  division  into  two  parts, 
distinct  in  colour  and  general  appearance,  the  one  white  and 
tendon-like,  the  other  glassy  and  transparent,  of  a  grayish-yellow. 
The  spindle-shaped  muscle-cells  of  the  former  generally  exhibit  a 
well-marked  longitudinal  striation  as  the  expression  of  fibrillated 
structure,  while  the  more  extended  and  flattened  fibres  of  the 
gray  part  are  often  striped  bi-obliquely  {Ostrea,  Anodonta,  etc.), 
and  in  many  cases  they  also  show  a  definite  transverse  striation 
{Lima,  Peden).  As  we  shall  see  later,  these  varieties  of  structure 
are  closely  allied  to  differences  of  function,  and  it  may  be  con- 
cluded, at  least  for  Pecten  and  Lima,  that  the  quick,  flapping 
movements  made  by  these  animals  are  served  by  the  striated 
part  of  the  adductor  muscle,  while  the  smooth  fibres  effect  the 
sustained  persistent  closure.  The  relation  between  cross-striation 
of  muscle -fibrils  and  rapidity  of  the  movement  engendered  is 
already  apparent  in  the  epithelial  muscles  of  Cnidaria,  where,  as 
we  have  stated,  the  comparatively  swift,  swimming  movements 
of  the  Medusa  are  produced  by  striated  fibrils.  This  also  accounts 
for  the  almost  universal  cross-striation  of  muscle -cells  in  the 
heart  and  masticatory  apparatus  of  Mollusca,  which  otherwise,  in 
regard  to  the  finer  structure  of  single  elements,  follow  closely  the 
forms  of  muscle-cells  described  above.  There  are  still  the  spindle- 
shaped,  freely  branched,  plexiform  fibre -cells,  which,  as  seen 
especially  in  transverse  section,  are  generally  rich  in  axial  sarco- 
plasm,  wholly  or  partially  surrounded  by  the  small  fibrillar  cortical 
layer.  The  latter  once  more  exhibits  frequently  a  distinct  radial 
striation  in  transverse  section,  representing  a  regular  alternation 
of  layers  of  fibrillated  substance  and  sarcoplasm.  Sometimes  the 
fibrils  (bundles  of  ?)  surround  the  plasma  bodies  of  the  cell  in  a 
single  row  of  dots  (Fig.  10,  a);  in  other  cases  the  cortical  layer 
seems  to  correspond  with  a  continuous  stratum  of  contractile 
substance. 

Even  a  superficial  comparison  of  cross-sections  through  the 
cardiac  or  masticatory  muscles  on  the  one  hand,  and  the  adductor, 
or  pedal,  muscle  respectively  on  the  other,  in  Lamellibranchs  and 
G-asteropods,  shows  that  the  relative  distribution  of  sarcoplasm, 
and  of  contractile  fibrils  separated  out  from  it,  varies  very  consider- 


ORGANISATION  AND  STRUCTURE  OF  MUSCLE 


19 


ably  in  the  two  cases.  While  in  the  cells  of  the  adductor  and 
pedal  muscles  the  formative  plasma  is  insignificant  in  comparison 
with  the  contractile  substance,  in  the  cardiac  and  masticatory 
muscles  it  preponderates.  Knoll,  who  first  investigated  these 
differences  systematically,  used  the  terms  a-plasmic  ("  clear  ")  and 
plasmic  ("  dark ")  to  designate  the  two  cases,  the  cells  of  the 
cardiac    and    masticatory  ^.r— ^  / '  -- 


C^' 


n 


:^ 


J 


w^ 


KJ'-^ 


"1 


'^ 


d 


:^:^. 


f\ 


V 


muscles  being  by  far  the 
richest  in  protoplasm,  and 
less  transparent.  These 
comparative  investiga- 
tions prove  beyond  doubt 
that  the  structural  ratio 
is,  like  cross-striation,  of 
functional  significance,  as 
also  appears  from  obser- 
vations on  the  muscles 
of  higher  animals  to  be 
discussed  below.  The 
cardiac  and  buccal  muscles 
have  obviously  more 
work,  and  more  persistent 
work,  to  do  than  the 
adductor  muscle  of  mol- 
luscs or  the  pedal  muscle 
of  snails,  w^hich  are  used 
less  frequently,  and  since 
the  formative  plasma 
stands,  as  will  be  shown, 
in  close  relation  with  the 
nutrition  of  the  contractile  substance,  we  can  readily  appreciate 
the  proportions  given. 

This  theory  is  substantially  confirmed  by  the  "float"  muscles 
of  Carinaria.  That  portion  of  the  foot  which  is  used  for  floating, 
and  is  in  constant  movement,  corresponds  both  in  the  cross- 
striation  of  the  fibrils,  and  the  abundance  of  its  sarcoplasm,  to 
the  type  of  dark  "  plasmic "  muscle-cells  characteristic  of  the 
buccal  and  cardiac  muscles  of  Mollusca.  Along  with  the  greater 
richness  of  sarcoplasm  there  is  often  a  more  or  less  definite 
coloration  of  the  muscular  elements.       The  cardiac  and  masti- 


-C> 


Fig.  10. — Transverse  section  of  muscle-cells  of  Mollusca. 
(Knoll.)  «,  Heart  of  Aplysia  lyunctata ;  h,  lieart  of 
Aplysia  limacina;  c,  masticatory  apparatus  of  Cari- 
naria; d,  longitudinal  view  of  muscle -cells  from 
buccal  mass  of  Aplysia  punctata. 


20  ELECTRO-PHYSIOLOGY  chap. 

catoiy   muscles   of   many  molluscs   are  yellow,   pink,  and  even 
deep  red. 

Knoll  discovered  a  remarkable  instance  of  "  plasmic  "  muscle- 
cells  among  Invertebrates,  in  the  thin  muscle-bands  of  the  mantle 
of  Salpa  (S.  maxima,  africana,  j^elesii).  The  cross-striped,  cylin- 
drical fibres  are  very  long,  with  conical  ends.  They  are  easily 
split  up  longitudinally  into  finer  bundles  and  fibrils,  owing  to  the 

excessive  abundance  of  sarcoplasm, 
which  intersects  the  plexus  of  fibrils, 
and  as  we  see  in  transverse  section, 
not  only  collects  in  the  axis  of  each 
fibre,  but  also  runs  out  in  wide, 
radial  tracts  towards  the  periphery, 
thus   dividing   the    contractile   and 

Fig.  ll.-Tiansverse  section  of  two  muscle-    distinctly  fibrillatcd  COrtical  Stratum 

cells  from  Scrijx(  pcZesii.    (Knoll.)  "^ 

into  separate  laminse  (Fig.  11).. 
The  same  plan  of  structure  is  here  to  some  extent  repeated, 
on  a  larger  scale,  that  prevails  in  the  far  more  delicate  radial 
striation  of  the  cortical  zone  of  muscle-cells  in  many  worms  and 
molluscs.  But  there  is  one  important  difference ;  the  contractile 
substance  is  no  longer  (as  in  all  previous  cases)  exclusively  at  the 
periphery  of  the  formative  cell,  but  appears  in  more  or  less  con- 
spicuous bundles  (muscle-columns)  within  the  central  sarcoplasm 
also.  Hence,  as  Knoll  has  pointed  out,  the  Salpa 
muscles  in  a  measure  represent  the  transition  to 
certain  arthropod  and  vertebrate  muscles,  in  which 
the  same  structural  arrangement  is  present.  A 
transverse  section  through  the  cardiac  muscles  of 
Crustacea  often  exhibits  an  unmistakable  similarity  fj(j_  12.— Trans- 
to    Salpa    in    disposition    of   sarcoplasm    and    con-     '^'eise  section  of 

.,  ,  --  -,  .  cardiac  mnscle- 

tractiie    substance,  except   that   the    sarcoplasm   is,     ceii  of  Lobster. 

where    possible,    even   more    richly    developed,   and     (^^^o^i-) 

all  the  "muscle-columns"  lie  within  the  formative  cell  (Fig.  12). 

The  unusual  quantity  of  protoplasm  is  explained  in  both 
cases  by  the  sustained  and  strenuous  work  which  is  served  by 
these  muscles. 

From  these  observations  we  may  conclude  that  there  is  no 
fundamental  difference  in  structure  between  the  different  muscle- 
cells  of  Invertebrates  (excepting  only  the  muscular  fibres  of 
Arthropoda) ;  whereas  among  Vertebrates  we  shall  find  striking 


ORGANISATION  AND  STRUCTURE  OF  MUSCLE 


21 


distinctions,  morphological  as  well  as  physiological,  between  the 
several  muscles — vegetative  and  animal.  This  is  admitted,  in  a 
general  sense,  by  the  common  division  of  vertebrate  muscles  into 
two  chief  groups — smooth  and  striated.  The  latter  are  technically 
opposed  as  muscle-^&?-c.s,  in  a  strict  sense,  on  account  of  their 
length,  to  muscle-cc^Zs  with  a  single  nucleus. 

The  smooth  muscles  and  striated  cardiac  muscle- 
cells  of  Vertebrates  are  the  natural  continuation  of 
the  uninucleated  muscle-cells,  smooth  and  striated, 
of  Invertebrates,  inasmuch  as  they  are  mainly  com- 
posed of  short,  usually  uninuclear,  elements  of  a 
more  or  less  distinctly  fibrillated  structure,  which, 
viewed  from  the  surface,  appear  for  the  most  part 
extended  and  spindle-shaped.  As  regards  smooth 
muscle-cells  in  particular,  they  are  not  infrequently 
drawn  out  into  fibres,  without  any  consequent 
increase  of  nuclei. 

In  cross-section  the  contractile  fibre-cells  appear 
either  rounded  (when  solitary),  or  flattened  by  the 
pressure  of  the  tightly -crowded  elements  into  a 
polygon  or  band -shaped  figure.  The  long,  oval, 
often  "rod -like"  nucleus  always  lies  in  the  middle 
of  the  cell,  surrounded  by  a  somewhat  richer  ac- 
cumulation of  formative  plasma.  Wherever  it  is 
possible  to  recognise  the  fibrillated  structure  (and 
this  is  by  no  means  invariable),  the  fibrils  appear  as 
a  multitude  of  fine,  smooth,  cylindrical  fibres,  running 
parallel  to  the  long  axis  of  the  cells,  and — as  seen  in 
transverse  section — bedded  in  a  seemingly  homo- 
geneous mass  of  sarcoplasm  (Fig.  13). 

But  while  in  nearly  all  the  cases  we  have 
been  considering  (of  Invertebrates)  the  fibrils  oc- 
cupied only  one  part  of  the  section,  surrounding 
the  sarcoplasm  in  a  ring  or  segment,  in  the  smooth  muscle 
of  Vertebrates  the  fibrils  are,  as  a  rule,  distributed  equally 
over  the  entire  surface.  It  is  highly  probable  that  fibrils  must 
also  exist  in  the  cases  where  it  has  so  far  been  impossible  to 
detect  them.  Sometimes  they  are  very  obvious,  and  appear,  e.g., 
in  the  fibres  of  the  frog's  stomach — Eugelmann  (12) — in  transverse 
section,  with  a  high  power,  as  little  circular  dots  or  spaces,  which 


W^ 


'r^ 


Fig.  13.— Central 
part  of  isolated, 
sniooth  muscle- 
cell  from  Frog's 
stomach.  (En- 
gelmami.) 


22  ELECTRO-PHYSIOLOGY 


do  not  vanish  on  raising  or  lowering  the  objective.  The  number 
of  fibrils  in  the  section  diminishes  towards  the  end  of  each  cell 
owing  to  their  unequal  length  (Engelmann).  The  fibrils  are  so 
highly  refractive  that  it  is  sometimes  difficult  to  recognise  the 
boundaries  of  adjacent  cells,  and  a  muscular  layer  of  the  kind  we 
are  describing  may  even  appear  as  a  single,  undifferentiated  mass 
of  fibrils. 

Smooth  muscle-fibres  do  not,  for  the  most  part,  occur  singly, 
but  arrange  themselves  into  bundles,  membranes,  or  bulky  masses. 
The  finer  and  more  delicate  bundles  of  muscle-cells  are  often  united 
into  a  net  with  wide  or  narrow  meshes,  each  adjacent  process  anasto- 
mosing with  its  neighbour  by  branches.  The  bladder  of  amphibia 
is  a  fine  illustration  of  such  a  net  with  wide  meshes.  Among 
Invertebrates  a  similar  plexus  of  uninuclear  muscle -cells  is 
found  in  the  heart  of  molluscs,  sucker  of  echinoderms,  etc. 

The  intestine  of  Vertebrates  is  the  best  example  of  the  struc- 
ture of  a  membrane  composed  of  smooth  muscle-cells.  Here  the 
arrangement  of  fibre-cells  in  two  layers,  crossing  at  right  angles, 
which  is  characteristic  of  most  hollow  organs  whose  walls  contain 
smooth  muscle-fibres,  is  very  conspicuous.  A  similar  arrangement, 
i.e.  a  longitudinal  and  a  circular  muscle-layer,  within  which  the 
axis  of  the  fibres  stand  vertically  to  each  other,  is  found  in 
the  ureter,  and  among  Invertebrates  in  the  cutaneous  muscular 
layer  of  worms. 

The  ccnatomical  relations  of  adjacent  muscle-cells  with  one  another 
is  a  point  of  great  interest.  A  number  of  physiological  facts 
pointed  to  direct  conductivity  from  cell  to  cell,  in  certain  smooth 
muscles,  long  before  histology  gave  substantial  support  to  the 
conjecture.  The  idea  of  a  direct  communication  by  means  of  proto- 
plasmic bridges  between  adjacent  cell-elements  (which  is  not  at 
all  a  new  hypothesis)  has  recently  obtained  extensive  confirmation 
on  the  botanical  side,  and  in  animal  histology  such  cell-bridges 
have  long  been  known  in  particular  objects  (bristle  or  prickle  cells 
of  the  epithelium).  Analogous  structures  have  recently  been 
described  in  smooth  muscle-cells  also.  In  the  transverse  section 
of  a  crowded  tract  the  single  elements  appear  to  be  united 
by  a  homogeneous  cement  substance,  which  gives  a  reaction 
similar  to  that  of  the  cement  substance  of  endothelium.  With 
certain  very  preservative  hardening  methods,  it  becomes  possible 
to  see  under  the  high  power,  that  the  single  cells  in  the  transverse 


I  ORGANISATION  AND  STRUCTURE  OF  MUSCLE  23 

direction  are   connected   by   fine   protoplasmic   bridges,  between 
which  are  small  intercellular  spaces  (Fig.  14). 

Common  as  is  a  marked  pigmentation  in  the  uninuclear, 
invertebrate  muscles,  it  is  but  seldom  that  we  find  definite  colora- 
tion of  the  smooth -muscle-cells  of  vertebrates.  The  bright  red 
muscles  of  the  gizzard  of  many  birds  are,  however,  an  exception,  as 
well  as  the  contractile  ^&re-ce//.s,  crowded  with  dark-brown  pigment 
granules,  in  the  iris  of  many  fishes  and  amphibia,  which,  according 
to  Steinach  (15),  owe  to  these  their  direct  excitability  to  light. 

We  must  not  omit  to  mention  certain  very  peculiar  figures 
obtained  from  smooth  muscle-fibres  that  have  been  fixed  during 
contraction.      A  highly  regular  transverse  striation  is  often  visible, 
due  presumably  to   swelling  from   the  contractions   that  follow 
one  another  at  regular  intervals.      The  figures  were  first  pointed 
out    by    Heidenhain     in    1861     (16),    and 
Drasche    has     recently     supplemented     our 
imperfect    knowledge    of    them   (17).       He      (^>- 
observed    a    regular   cross -striation    in    the 
individual     fibre -cells     of     the     contracted   C -^     * 
muscular     coat     of     the     poison  -  gland     of     '^-  ^        -  ^  _ 
Salamander,  resulting  from  a  delicate  trans-  fig.  i4.— Transverse  section 

1      T      •  1     ,  •  of  the  bladder -muscles  of 

verse  groovmg,  or  marked   mvolution,  pro-     R^t  (ceii-bridges).    (From 
duced    by    the    contraction    of    the    lower     G.deBmyne,Arcii.deBioi., 

.  „     .  -  o-      -1  1    T       4-  vanBeneden,vol.  xii.  1S92.) 

surface  oi  the  muscle,  bmiilar  very  delicate 
fiffures  were  observed  in  the  muscle-cells  of  a  cat's  intestine 
that  had  been  hardened  in  alcohol  (Biedermann).  The  sharply 
defined,  highly  refractive,  transverse  swellings  gave  an  im- 
pression of  local  (fixed)  waves  of  contraction,  such  as  occur 
occasionally  in  certain  striped  muscles. 

Apart  from  the  Arthropoda,  in  which  uninuclear  muscle- 
cells  seem  to  be  altogether  wanting,  the  existence  of  tme  cross- 
striation,  i.e.  disposition  of  each  single  fibril  in  layers  of  different 
optical  relations,  would  appear  from  the  foregoing  to  be  compara- 
tively rare  in  muscle-cells ;  its  physiological  significance  has 
already  been  indicated. 

The  much  commoner  oblique  striation  stands,  as  we  have  said, 
in  no  sort  of  relation  to  the  transverse  striae,  since  the  single  fibrils 
are  not  further  differentiated,  and  deviate  in  direction  only  from 
the  normal.  We  find  it  impossible  to  subscribe  to  the  theory 
recently  advanced  by  Knoll  to  the  effect  that  there  is  no  sharp 


24 


ELECTRO-PHYSIOLOGY 


distinction  between  oblique  striation  and  cross-striation  proper, 
so  that  one  and  the  same  cell  may  present  oblique  or  transverse 
striee  under  different  conditions.  It  seems  more  probable  that 
the  effect  is  due  partly  to  different  states  of  contraction 
in  adjacent  fibrils,  partly  to  a  longitudinal  displacement 
(transposition)  of  the  fibrils. 

In  Vertebrates  also,  in  the  adult  state,  it  is  exceptional  to 
find  transversely  striated  uni-  or  binuclear  muscle-cells ;  they 
occur  in  cardiac  muscle,  and  in  a  peculiar  development  of 
the  endocardium  of  ruminants,  horses,  pigs,  and  other  mammals, 
and  in  certain  birds.      As  a  rule,  the  elements  of  cardiac  muscle 

either  resemble  the 
smooth,  spindle- 
shaped  fibre-cells 
(fishes,  amphibia), 
though  they  ex- 
hibit many  irregu- 
larities of processes 
and  branches,  or 
form  somewhat  ir- 
regular cylindrical 
or  flattened  cell- 
bodies,  anastomos- 
ing at  the  ends 
with  the  adjacent 
elements  in  a  net- 
work of  branches 
by  means  of  short  broad  processes,  of  which  the  smooth  superficies 
are  closely  applied  together  (mammals,  birds,  reptiles)  (Fig.  15). 
In  many  cases  the  component  cells  are  still  clearly  visible  ;  in 
others  they  have  disappeared,  or  become  hard  to  recognise. 

These  principal  types  of  cardiac  muscle  are  connected  by  many 
transitional  forms.  As  so  often  in  the  elements  of  smooth 
muscle,  the  cardiac  muscle-cells  form  inter  se  a  physiological  as 
well  as  an  anatomical  continuum,  being,  like  many  epithelia  and 
endotheha,  united  by  a  cement  substance,  which  stains  black 
with  AgNOg,  and  through  which  transmission  of  the  excitatory 
process  is  apparently  effected.  Whether  there  is  here  the 
same  anastomosis  of  adjacent  cell-bodies  by  bridges  of  protoplasm 
as  in  many  smooth  muscles,  has  not  been  determined. 


Fig.  15.- 


-Isolated  cells  of  cardiac  muscle.    A,  from  Man  ;  B,  from 
Rana  temporaria.    (Schiefferdecker.) 


ORGANISATION  AND  STRUCTURE  OF  MUSCLE 


25 


The  arrangement  of  the  cross -striated  fibrils  within  the 
formative  plasma  (sarcoplasm)  is  very  remarkable.  The  sarco- 
plasm  is  so  abundant  both  in  vertebrate  and  invertebrate  animals, 
that  the  otherwise  non-membranous  cardiac  muscle-cells  come 
under  the  category  of  "  dark "  muscles,  with  which  their 
easy  separation  into  fibrils  and  bundles  of  fibrils  also  coincides. 
In  transverse  section  the  cardiac  muscle -cells  of  Fishes  and 
Amphibia  exactly  carry  on  the  type  of  Cephalopods  and  Gastro- 
poda, each  spindle -cell  exhibiting  a  richly  developed,  central, 
medullary  substance  surrounding  the  nucleus,  and  enclosed  in  its 
turn  by  the  transversely  striated  fibrils  of  the  cortical  substance, 
which  are  often  arranged  in  radial  strata. 

The  heart  of  Eeptiles  and  Birds  is  characterised  by  the  same 
structure;  the  contractile  cortex  of  the  latter  in  particular 
frequently  exhibits  distinct  radial 
striation.  In  Mammals  also  the 
elements  of  the  cardiac  muscle 
(which  is  here,  as  in  other  verte- 
brates, of  a  deep  red  colour) 
are  among  the  most  richly  proto- 
plasmic parts  of  the  body.  The 
distribution  of  sarcoplasm  and 
fibrils  closely  resembles  the 
spindle-cells    of    Salpa    described 

above ;  the  bundles  of  fibrils  (Kolliker's  "  muscle-columns  ")  not 
only  form  a  peripheral  cortical  zone,  but  are  developed  within  the 
central  nucleated  axial  plasma  (Fig.  16).  The  plasma  itself  is 
usually  accumulated  round  the  nucleus,  which  lies  somewhat 
toward  the  centre  of  each  cell.  The  bundles  of  fibrils  (muscle- 
columns)  present  considerable  variations  of  form  and  arrangement 
in  different  mammals.  The  radial,  band-shaped  bundles  of  fibrils, 
striped  in  cross-section,  with  which  we  are  so  familiar  in  Inverte- 
brates, and  also  in  certain  muscles  of  the  lower  Vertebrata,  but 
which  appear  only  in  the  heart  of  Mammals  (dog,  porpoise),  are 
very  frequent.  Often,  besides  these  band-shaped  muscle-columns, 
which  figure  in  transverse  section  as  a  radially  striated,  laminar, 
cortical  zone,  another  prismatic  section — rounded  or  polygonal 
— appears  in  the  centre  of  the  muscle-cell  (dog,  man)  (Fig.  16). 
And,  in  conclusion,  there  are  many  examples  (pig)  in  which  these 
last  only  are  present. 


Fig.  16. — Transverse  section  of  cardiac 
muscle-cells — Man.     (Kolliker.) 


26  ELECTRO-PHYSIOLOGY 


Generally  speaking,  therefore,  it  may  be  said  that,  in  regard 
to  histological  structure,  the  cardiac  muscles  exhibit  great 
similarity  with  certain  muscles  of  the  lower  animals  and  the 
developing  stages  of  cross-striated,  multinuclear  muscle-fibres, 
and  are  thus  in  a  certain  sense  embryonic  in  character.  This 
applies  not  merely  to  the  striking  abundance  of  sarcoplasm,  but 
also  to  the  form  and  arrangement  of  the  muscle-columns,  and 
central  situation  of  the  nucleus. 

The  elements  of  cardiac  muscle  in  Vertebrates,  in  particular 
of  mammals,  together  with  the  cross -striated  uninuclear  cells 
of  Invertebrates,  form  the  transition  to  the  type  of  muscle  which 
is,  anatomically  and  physiologically,  the  most  highly  developed. 


Cross-steiated,  Multinuclear  Muscle-Fibres 

Among  Invertebrates  these  occur  in  Arthropoda  only ;  in 
Vertebrates,  collectively,  they  form  the  chief  bulk  of  muscle. 

At  one  time  it  was  supposed,  chiefly  on  account  of  the 
multiplicity  of  nuclei  in  striped  muscle-fibres,  that  these  re- 
presented a  fused  series  of  many  cells  (a  "  syncytium  "),  but  it  is 
now  admitted  that  each  striated  muscle-fibre  is  equivalent  to  a  single 
cell,  from  which,  indeed,  it  has  developed.  At  first  these  are 
uninuclear,  spindle-shaped  cells,  which  grow  rapidly  longer,  while 
the  nucleus  increases  by  repeated  division.  Subsequently  the 
elongated,  multinuclear  spindles  become  not  only  longer,  but  much 
wider,  while  a  gradual  differentiation  of  striated  fibrils  is  pro- 
ceeding from  the  increasing  bulk  of  protoplasm  (sarcoplasm). 
These  fibrils,  viewed  longitudinally,  or  better  in  transverse  section, 
do  not  occupy  the  entire  thickness  of  the  fibre,  but  arrange  them- 
selves superficially  as  a  tubular  sheath,  or  (in  many  of  the  lower 
vertebrates)  as  a  segment  lying  to  one  side,  so  that  the  nucleated, 
formative  (sarco-)  plasma  lies,  as  it  were,  enclosed  in  a  canal  or 
furrow  (Fig.  17). 

A  toivporary  relation  thus  arises  between  the  latter  and  the 
differentiated  fibrils,  which  is  altogether  analogous  to  the  constant 
distribution  of  the  permanently  uninuclear  myoblasts  of  most 
invertebrates.  As  development  progresses  the  peripheral  layer 
of  fibrils,  at  first  extremely  attenuated,  increases  in  bulk  at 
the  expense  of  the  sarcoplasm,  so  that  eventually  the  ratio  is 


I  ORGANISATION  AND  STRUCTURE  OF  MUSCLE  27 

reversed ;  the  fibrils  form  the  chief  bulk  of  the  fully-developed 
muscle-fibre,  while  the  I'emains  of  the  formative  plasma,  together 
with  many  nuclei,  is  interspersed  between  the  mass  of  fibrils,  in 
varying  bulk  and  disposition.  Each  fibre  thus  presents  a  long, 
cylindrical,  prismatic  figure,  with  conical  or  blunted  ends.  The 
fibres  are  usually  undivided,  but  may  branch  more  or  less  freely 
with  many  nuclei,  and  even  form  an  anastomosis. 

The  multinuclear,  striated  muscle-fibres  must  be  reckoned 
among  the  largest  cells  with  which  we  are  acquainted.  Accord- 
ing to  Kolliker  the  uninuclear,  spindle-shaped  myoblasts  of 
the  human  embryo,  seven  to  eight  weeks  old,  are  already  132  to 
176  yu-  in  length,  and  over  300  fx  a  little  later. 

In  adult  muscle-fibres,  Felix  finds  some  that  certainly  exceed 
12  cm.  in  length,  to  which  we  must  add  that  the  fibres,  even 
thus,  were  not  at  their  greatest  extension.  The  bulk  is  relatively 
very   small  ;    it   is   greatest  ^ 

at  an  early  stage  of  develop- 
ment. According  to  Felix, 
human  muscle-fibres  at  the 
third  month  attain  the  con- 
siderable diameter  of  1 3  to  1 9 
/x  ;  these  dimensions  are  rare 

in  older  embryos,  and  only  re-     Fig.  it.— Euibrydnie  muscle-libres.    o,  Man  ;  &,  Frog. 

appear  in  the  new-borninfant. 

The  length  of  the  single  primitive  fibril  is  in  no  regular  ratio 
with  the  length  of  the  muscle  developed  from  it.  Whereas 
formerly  it  was  supposed  that  the  muscle-fibres,  generally  speak- 
ing, corresponded  in  length  with  the  coarser  muscle-bundles, 
it  is  now  known  that  numerous  fibres,  particularly  in  the 
longer  muscles,  terminate  freely,  are  shorter,  i.e.,  than  the  whole 
muscle.  Both  free  ends  accordingly  may  be  pointed,  and  the 
whole  fibre  spindle-shaped,  or  one  end  only  may  be  free,  and  the 
other  blunt  and  connected  with  the  tendon.  In  small  muscles, 
on  the  contrary,  according  to  Kolliker,  all  the  fibres  run  the 
length  of  the  entire  muscle,  and  are  generally  rounded  off  at  both 
ends. 

Nearly  all  cross -striated,  uninuclear  muscle-fibres  (except- 
ing only  in  certain  Arthropoda)  possess  a  distinct  sheath,  the 
sarcolemma,  which  consists  of  a  fine,  transparent,  structureless 
membrane,  lying  next  to,  and  closely  investing  the  contents  of. 


28  ELECTRO-PHYSIOLOGY 


the  primitive  bundle  (sarcoplasm  with  nuclei  and  fibrils) ;  it  can, 
therefore,  only  be  seen  clearly  in  places  where,  from  rupture  of 
the  fibres,  or  any  other  cause,  the  contents  of  the  muscular 
sheath  have  shrunk  back  from  the  wall,  or  where,  conversely,  the 
latter  has  risen  up  in  a  bladder  (imbibition  of  water).  The 
sarcolemma,  which  Kolliker  reckons  in  vertebrates  as  a  true  cell- 
membrane,  may  be  seen  even  at  an  early  stage  of  development 
in  the  muscle-fibres  as  a  very  delicate  integument;  other 
authors  regard  it  as  a  product  of  the  connective  tissue  that 
surrounds  the  muscle-cell. 

In  accordance  with  the  usual  disposition,  multinuclear 
muscle-fibres  severally  exhibit  more  or  less  distinct  transverse 
strice,  at  right  angles,  i.e.,  to  the  axis  of  the  fibre,  a  characteristic 
common  also  to  many  uninuclear  muscle-cells  of  invertebrates 
and  vertebrates,  and  due,  as  will  be  shown,  to  the  same  cause  in 
both  instances. 

In  addition  to  the  transverse  strife,  a  longitudinal  striatio7i 
(derived  from  the  fibrillated  structure)  is  nearly  always  apparent ; 
it  may  be  excessively  fine,  or  may  separate  the  fibres  into  com- 
paratively large  bundles. 

The  relative  distinctness  of  the  transverse  and  longitudinal 
strite  at  a  given  moment  varies  very  considerably  in  different 
muscle-fibres.  In  many  cases  the  cross-striation  is  hardly  visible, 
while  the  longitudinal  strite  are  clearly  marked :  at  other  times 
the  opposite  appears.  Different  parts,  indeed,  of  one  and  the 
same  fibre  may  vary  in  this  particular.  This  is  essentially 
dependent  upon  the  relation  between  the  contractile  fibrils  and 
the  interfihrillar  sarcoplasm,  which  (as  many  recent  observations 
have  established)  may  vary  enormously,  alike  in  the  muscles  of 
different  animals,  and  in  the  different  muscles  of  the  same  species. 
As  was  stated  above,  the  examination  of  cross-sections  gives  the 
best  and  surest  conclusions.  The  salient  feature  under  all 
conditions  is,  in  the  fully-developed  fibre  also,  the  unequal  dis- 
tribution over  the  surface  of  the  section.  The  fibrils  are  arranged 
in  larger  or  smaller  bundles  ("  muscle-columns "),  separated  by 
more  or  less  bulky  discs  (strise,  from  the  longitudinal  aspect)  of 
sarcoplasm  {interstitial  substance,  interfibrilla.r  siibstoMce,  sarcogleia), 
as  in  so  many  smooth  and  cross -striated  uninuclear  muscle- 
cells.  The  more  abundant  the  sarcoplasm,  the  easier  the  division 
of    a    primitive    bundle    into    "  muscle-columns,"  i.e.    bundles    of 


I       '  ORGANISATION  AND  STRUCTURE  OF  MUSCLE  29 

fibrils,  which  by  proper  methods  can  again  be  spht  up  into 
the  true  elementary  fibrils.  As  in  the  uninuclear  muscle- 
cells,  the  multinuclear  m.\\^Q\e- fibres  fall  in  the  main  into  two 
distinct  forms  or  types  of  "  muscle-columns."  These  are  either, 
as  in  many  invertebrate  muscles,  flat  band-like  bundles,  composed 
of  a  single  row,  or  some  few  rows,  of  fibrils  only,  or  (as  is  more 
common)  the  bundles  appear  to  be  cylindrical  or  prism-shaped, 
i.e.  circular  or  polygonal  in  cross-section. 

When,  as  in  the  majority  of  cases,  the  prismatic  "muscle- 
columns  "  are  separated  by  a  comparatively  insignificant  mass  of 
"interstitial  substance,"  a  mosaic  of  polygonal  arese  appears  in 
transverse  section — as  first  described  by  Cohnheim ;  whence, 
therefore,  the  name  of  Cohnheim s  Arece  (Fig.  18,  a,  b). 


1*^4*     »  ^       ^      vf 


Fig.  18.— a,  Transverse  section  of  muscle-fibre  of  Rabbit  (bundles  of  fibrils  dark,  sarcoplasm  clear). 
(Kollilcer.)  &,  Transverse  section  of  muscle-flbre  of  Frog,  showing  on  the  left  cross-sections 
of  the  fibrils.    (Schiefierdecker.) 

It  is  questionable  whether  the  sarcoplasm  that  surrounds  the 
muscle-columns  penetrates  also  between  the  individual  fibrils  : 
KoUett  disputes  it ;  Kolliker  assumes  a  minute  amount  of  inter- 
stitial matter,  identical  with  the  sarcoplasm — it  can  only  be 
identified  under  a  very  high  power,  and  forms  an  investing  sheath 
along  the  entire  length  of  each  fibril. 

From  this  last  point  of  view  each  muscle-fibre  must  be  re- 
garded as  a  bundle  of  fibrils  which  are  held  together  by  an 
uneven  accumulation  of  intermediary  substance.  "  According  as 
this  accumulation  is  more  or  less  abundant,  the  muscle-columns 
are  more  or  less  well  defined,  larger  or  smaller  "  (K^olliker). 

The  comparative  proportion  of  the  two  chief  constituents  of  a 
muscle-fibre,  i.e.  the  fibrils  (Kiihne's  rhabdia)  and  the  sarcoplasm, 
varies,  as  we  have   said,  in    different   animals,  and  in  different 


30 


ELECTRO-PHYSIOLOGY 


muscles  of  the  same  animal;  and  the  same  is  true  of  the 
position  of  the  nucleus.  Two  groups  of  striated  fibres  can  again 
be  distinguished  in  vertebrates,  i.e.  those  which  have  much,  and 
those  which  have  little,  sarcoplasm.  The  fibres  of  the  first  group, 
generally,  look  rather  dark  when  examined  with  the  microscope, 

T^  owing  to  the  large  num- 
ber of  interstitial  "  gran- 
ules "  with  which  the 
'-'Sp  sarcoplasm  is  studded ; 
the  cross -striae  are  in- 
distinct, the  longitudinal 
well  marked.  The  a- 
plasmic  fibres,  on  the 
other  hand,  are  clearer 
and  transparent,  with 
sharp  transverse  striae. 
In  the  same  sense,  we 
structure      of     the     uni- 


FiG.  19. — Transverse  section  of  two  float-muscles  oi  Hippo- 
campus.  (Ms),  Bundles  of  fibrils  (nmscle- columns) ; 
(Sp),  sarcoplasm.     (Rollett.) 


—ife 


have  already,  ia  describing  the 
nuclear  muscle -cells  of  invertebrates  and  vertebrates,  had 
occasion  to  distinguish  between  clear  and  dark,  plasmic  and 
a-plasinic  elements;  cardiac  muscle -cells  in  particular  being 
universally  dark  and  plasmic.  The  float  muscles  of  the  Sea- 
horse (Hippocampus)  exhibit 
a  peculiarly  typical  example 
of  plasmic,  multinuclear 
muscle-fibres  in  the  Verte- 
brates. In  transverse  sec- 
tion the  flat  bands  of  muscle- 
fibrils  (muscle-columns)  are 
seen,  as  in  the  muscles  of 
Salpa,  or  the  cardiac  muscle 
of  Crustacea  {siq^ra),  form- 
ing irregular  groups  and 
columns  in  the  sarcoplasm, 
which  is  here  excessively  abundant,  and  presents  a  thick 
cortical  layer  in  which  the  nuclei  are  embedded  (Fig.  19). 
Similar  bands  of  muscle-columns  are  found  in  the  lateral  muscles 
of  the  carp,  which  are  also  characterised  by  an  abundance  of 
nucleated  sarcoplasm  lying  close  under  the  sarcolemma  (Fig.  20). 
Other  muscle-fibres  (lateral  trunk-muscles)  in  the  same  fish — 


Pig.  20. — Transverse  section  of  lateral  muscle-fibres 
of  Carp.     (Kolliker.) 


ORGANISATION  AND  STRUCTURE  OF  MUSCLE 


31 


like  many  cardiac  muscle-cells  (man,  horse) — show  a  peripheral 
layer  of  the  flat  bands  of  fibrils,  while  the  interior  is  filled  with 
polygonal  bundles.  The  nuclei  are  again  embedded  in  the  layer 
of  sarcoplasm  that  surrounds  the  entire  fibre.  A  corresponding 
structure  is  found  in  the  same  muscles  of  other  fishes. 

In  the  hig-her  vertebrates,  a  transverse  section  of  the  skeletal 
muscle  usually  exhibits  polygonal  arese,  separated  by  a  very  small 
quantity  of  sarcoplasm  (Cohnheim's  Arece,  Fig.  18,  a).      But  there 


Fig.  21. — a,  Transverse  section  of  Pectoralis  major  in  Falcon  ;  b,  ib.  Goose  ;  c,  ib.  Hen.    (Knoll.) 

are  still  distinctions  corresponding  with  dark  and  clear  muscles, 
greater  or  less  abundance  of  sarcoplasm.  In  Amphibia  the  clear 
fibres  usually  predominate  ;  the  throat  muscles  of  batrachians  are, 
however,  an  exception.  Knoll  also  found  a  considerable  develop- 
ment of  sarcoplasm  in  the  jaw  muscles  of  reptiles,  and  the  limb 
muscles  of  Lacerta  and  Cistudo.  In  birds,  on  the  other  hand, 
the  dark,  plasmic  fibres  prevail,  and  constitute  the  pectoral 
muscles  used  in  flight.  In  the  hen  the  muscles  of  the  breast 
and  back  consist,  however,  exclusively  of  light  fibres,  which  are 


32 


ELECTRO-PHYSIOLOGY 


again  in  a  minority  in  the  same  parts  of  the  goose  and  pigeon, 
while  they  are  wholly  wanting  in  the  falcon,  crow,  and  sparrow 
(Pig.  21). 

From  birds  onwards  the  dark  fibres  are  usually  in  the  ascend- 
ant. According  to  EoUett  the  elements  of  the  skeletal  muscles 
of  the  bat  are  peculiarly  rich  in  sarcoplasm.  In  transverse 
section  it  appears  as  a  number  of  coarse,  irregular  knots,  drawn 
to  one  side  or  the  other,  and  united  by  fine,  slender  bridges  of 
protoplasm ;  the  muscle-columns  lie  in  the  intermediate  spaces 
(Fig.  22,  a). 

The  superficial  aspect  of  the  fibres  is  correspondingly  coarse. 


^>  s;  s  S  S  #  S  •  S  J 

Fig.  22. — Transverse  and  longitudinal  sections  of  tlie  muscle-fibre  of  Bat.    Sarcoplasm  clear, 
fibril-bundles  (muscle-columns)  dark.    (Rollett.) 


with  longitudinal  strise,  due  to  the  alternation  of  sarcoplasm  and 
muscle-columns  (Fig.  22,  l).  In  most  other  mammals  the  dark 
and  relatively  plasmic  fibres  are  intermixed  with  clear  fibres  in 
the  skeletal  muscles.  Knoll  finds  that  the  optic,  masticatory, 
and  respiratory  muscles  (in  particular  the  diaphragm)  are  specially 
rich  in  dark  fibres.  In  almost  all  vertebrates  the  dark  are 
smaller  than  the  clear  fibres.  This  is  well  shown  in  transverse 
sections  of  muscles  containing  both  kinds  of  fibres  (pectoral 
muscle  of  pigeon,  most  muscles  of  amphibia  and  mammals)  (Fig. 
21).  Moreover,  the  "  dark "  fibres  in  many  cases  are  charac- 
terised by  their  deep  red  colour,  while  the  "  clear "  fibres  are 
paler.  The  dark  lateral  muscles  of  many  fish,  e.g.,  and  the  float 
and  cardiac  muscles,  are  intensely  red ;  in  Ptana  escul.  and  tem}^. 
also,  the  muscles  of  the  throat  and  heart  are  dark  and  red. 


I  ORGANISATION  AND  STRUCTURE  OF  MUSCLE  33 

The  striated  muscles  of  mammals  are  mostly  red,  and  (with 
the  exception  of  the  cardiac  nmscle-cells,  and  the  muscles  of  the 
bat,  which  are  uniformly  dark)  contain  a  mixture  of  clear  and 
dark  fibres. 

The  variations  of  colour  in  different  muscles  are  particularly 
striking  in  the  domestic  animals.  Every  one  knows  the  "  white 
meat "  of  breast  and  back  in  the  common  fowl,  which  consists 
exclusively  of  clear  fibres,  while  the  leg-muscles  are  red  and 
dark  in  colour.  In  tame  rabbits  and  guinea-pigs  also,  white  pale 
muscles  occur  along  with  the  strictly  red  of  the  heart,  diaphragm, 
etc. ;  and  here  again  dark  fibres  preponderate  in  the  one  case,  and  f 
clear  in  the  other,  but  the  degree  of  colour  and  quantity  of  proto- 
plasm are  not  always  proportional.  Thus  in  the  pigeon  the  red ' 
wing-muscles  are  composed  chiefly  of  dark,  the  equally  red  leg- 
muscles  of  clear  fibres,  and  in  the  rabbit  also  there  is  little  differ- 
ence in  amount  of  protoplasm  between  the  dark  red  soleus  and  the 
pale  adductor  magnus  muscles.  In  Triton  and  Salamandra,  the  leg- 
muscles  are  reddish,  but  distinctly  dark  in  single  fibres  only ;  the 
rest  of  the  muscles  are  pale  and  clear.  Eanvier  also  finds  a  dis- 
tinction in  number  and  distribution  of  the  nuclei  between  red 
and  pale  muscles,  but,  according  to  Knoll,  no  general  rule  can  be  laid 
down.  In  all  mammalian  muscles  investigated  by  him,  the  nuclei 
are  "predominantly"  set  round  the  periphery  of  the  fibre,  but  there 
are  always  individual  fibres  with  instanding  nuclei,  and  this  not 
only  in  the  red  muscles  as  stated  by  Eanvier,  but  in  the  definitely 
pale  muscles  also  (adductor  magnus  of  rabbit).  Generally  speak- 
ing, the  centrally-situated  nucleus  corresponds  with  a  low  grade  of 
development  in  muscle-fibre,  and  is  therefore  the  rule  only  in  fishes 
and  amphibia,  in  which  last  many  nuclei  are  often  strung  together 
in  a  longitudinal  series,  while  in  the  muscle-fibres  of  birds  and 
mammals  the  nuclei  are  generally  placed  at  the  periphery,  close 
under  the  sarcolemma ;  but  here  again  there  may  be  exceptions. 

Within  the  sarcoplasm,  which,  as  follows  from  its  develop-    ; 
ment,  represents  the  original  formative  plasma,  lie  the  structures   I 
described  by  Kolliker  as  "  interstitial  granules,"    and  these,  in 
virtue  of  their  strong  refractibility,  are,  when  accumulated  between    i 
the  bundles  of  fibrils,  the  cause  of  the  "  dark,"  opaque  properties 
of  certain  muscle-fibres. 

The  greatest  variety  of  mass-disposition,  and  relative  propor- 
tion of  sarcoplasm  and  fibrils,  is  exhibited  by  the  striated  muscle- 

D 


34 


ELECTRO-PHYSIOLOGY 


filrcs  of  the  Arthropoda,  which,  anatomically  and  functionally,  have 
reached  the  highest  development.  In  view  of  certain  important 
differences  of  structure,  that  must  correspond  with  no  less 
simificant  differences  in  function,  two  main 
types  of  striated  fibres  may  be  distinguished, 
which,  although  they  exist  only  in  certain  of 
the  Arthropoda,  are  always  differently  localised. 
These  are  what  KoUiker  has  termed  "  typical " 
and  "  a-typical "  fibres ;  the  first  presenting 
essentially  the  same  organisation  as  the  fibres 
of  vertebrates,  while  the  second,  which  exist 
only  in  the  thoracic  muscles  of  winged  insects, 
are  very  divergent  in  structure.     With  regard 

Pig.    23.— Transverse    sec-  "^  ^  .... 

tionofmuscie-flbre,  Mya  to  the  first  type,  wc  may  distinguish,  as  in 

?— iei^iumn.^^''''"'  vertebrates,    fibres    with     prismatic    columns 

(Sehiefferdecker.)  (polygoual   in   trausvcrsc  sectiou),  and  fibres 

with   flat   bands    of  fibril   bundles.      Tlie   muscles    of  Crustacea 

(Astactis)    are    a    typical    example    of    the    first,    exhibiting    in 

cross-section  just  such  a  mosaic  of  polygonal   Cohnheim's  arese 

as  we   find   in   most  vertebrate   muscle-fibres  (Fig.   18,  h).      The 

sarcoplasm,    however,    is 

always    more    abundant ; 

it   separates    not   merely 

single  muscle-columns  but 

whole    groups    of    them, 

forming  (as  in  the  muscles 

of  Amphibia)    thick   and 

usually  nucleated  lamellae 

in    the    interior    of    the 

muscle :    the    sarcoplasm 

also   forms    a   continuous 

sheet,  greater  or  less  in 

thickness, immediately  be- 
neath the  Sarcolemma  (as    Fig.  24.— Transverse  section  of  muscle-fibre,  HydroiMlus. 

in  certain  musclp-fibrPS  nf  Sarcoplasm  clear,  muscle-columus  dark.    (RoUett.) 

fishes).  The  muscles  of  Maj'a  Squmado  (Fig.  23)  afford  another 
elegant  illustration  of  this  structure  of  fibre.  In  Beetles  the 
polygonal  prismatic  muscle-columns  are  very  prominent ;  the 
sarcoplasm  lies  evenly  distributed,  or  is  unequally  heaped  up  in 
parts  of  the  transverse  section. 


I  ORGANISATION  AND  STRUCTURE  OF  MUSCLE  35 

Sometimes  the  sarcoplasm  will  be  found  only  in  the  centre  of 
the  fibre,  densely  heaped  up  in  a  round,  or  slit-like,  cavity.  The. 
muscle-columns,  which  in  such  cases  form  broad  bands,  are  set 
radially  round  the  central  mass  of  nucleated  protoplasm,  like 
the  leaves  of  a  book,  separated  only  by  very  fine  lamellae  of 
sarcoplasm,  a  disposition  already  familiar  to  us  in  the  uni- 
nuclear muscle -cells  of  many  invertebrates.  According  to 
Eollett,  the  direct  transition  to  this  most  characteristic  structure 
in  the  muscles  of  the  Dytiscidse  is  found  in  numerous  little 
Carabidse,  e.g.  Brachinus,  and  the  common  wasp,  where  the 
muscle -fibres  are  more  or  less  elongated  in  cross -section,  and 
present  radially  situated  Cohnheim's  arese  in  their  longer 
diameter. 

Eetzius  (19)  was  the  first  to  describe  the  very  delicate  trans- 
verse figures  exhibited  by  the  muscle-fibres  of  DytiscAis  marg.  in 


Fig.  25. — «,  Transverse  section  of  muscle-fibres  (extremities)  of  Dytiscus  iiutrginalis ;  b,  part  of  tlie 
section  on  application  of  dilute  acids.  Small  secondary  strata  denoting  the  cross-sections 
of  single  fibrils  appear  between  the  primary  strata  of  sarcoplasm.    (v.  Limbeck.) 

gold  chloride  preparations,  to  which  we  shall  return  presently  (Fig. 
2  5).  But  his  interpretation  of  the  figures  (adopted  later  by  Bremer, 
V.  Gehuchten,  and  Eamon  y  Cajal)  must  be  regarded  as  fallacious, 
chiefly  on  the  groimd  of  the  classical  researches  of  Eollett. 
Eetzius  conceived  the  central  muscle-nuclei  with  the  surrounding 
sarcoplasm  to  be  true  cells  (analogous  to  Schultze's  muscle- 
corpuscles)  with  excessively  fine  processes,  and  believed  that  these 
filiform  nets,  stretched  horizontally  in  the  muscle -fibre,  were 
arranged  at  regular  intervals  one  beyond  the  other,  the  fibrils 
lying  in  their  meshes.  On  this  assumption,  the  outlines  of 
Cohnheim's  areee,  whatever  their  individual  shape,  must  be  viewed 
not  as  the  optical  expression  of  the  sarcoplasm  accumulated  at 
the  edges  of  the  muscle-columns,  forming  a  network  of  partitions 
right  along  the  muscle-fibres,  but  as  the  superficial  aspect  of  the 


36 


ELECTRO-PHYSIOLOGY 


superposed  nets  of  filaments,  consisting  of  the  cell  processes  of 
the  muscle-corpuscles,  and  only  connected  longitudinally  by  fine, 
small  fibres.  Apart,  however,  from  the  fact  that  the  appearance 
of  a  muscle-fibre  in  optical  transverse  section  must  then  vary 
with  alterations  of  the  objective,  according  as  the  cross-section  of  a 
fibre-plexus,  or  the  space  between  two  such,  is  focussed  (when  in  the 
first  case  Cohnheim's  areee,  in  the  second  a  mere  system  of  dots, 
corresponding  with  the  cross-sections  of  the  connecting  longitudinal 
fibres,  would  appear — which  never  is  the  case),  the  comparative 
study  of  the  development  and  structure  of  fully  developed  muscle- 
fibres  and  cells  of  different  animals  appears  to  us  to  be  conclusive 
evidence  against  this  theory.      For  the  rest,  it   is  sufficient  to 

quote  the  masterly  criticisms 
of  Eollett  (20). 

The  muscles  of  Flies  ex- 
hibit very  peculiar  structural 
relations  (Fig.  26).  In  trans- 
verse section  the  bundles  of 
fibrils  are  once  more  flat  and 
band-like,  and  usually  consist 
of  a  single  layer  of  fibrils 
only.     These,  however,  are  so 

Fig.  26.— Transverse  section  of  striated  muscle-fibres  dispOScd     in     SCricS     that     twO 
of  Mnsca  domestica      A    Low  power;  B,  higbly  ^|  ^^ 

magnified ;     ills,    bands    of    muscle  -  columns  v      v>v^ 

(bundles  of  fibrils) ;   Sp,  sarcoplasm.    (Schieft'er-  formed         fitting        illtO        OllC 

another,  and  separated  by 
strata  of  protoplasm,  with  which  they  are  also  filled  and  sur- 
rounded. The  nuclei  lie  in  the  innermost,  axial,  plasma  cylinder, 
as  appears  in  the  longitudinal  section  of  such  a  fibre.  These  few 
examples  will  give  an  approximate  idea  of  the  multiplicity  of 
figures  in  cross -section  in  the  "  ty23ical "  arthropod  muscles. 
Before  we  pass  on  to  the  structure  of  the  "  a-tyfical "  wing- 
muscles  (thoracic  fibrils)  of  insects,  the  question  as  to  the  com- 
position of  "  muscle-columns  "  out  of  "  fibrils  "  must  detain  us  for 
a  few  moments.  In  Insect  as  in  Vertebrate  muscles,  the  direct 
proof  is  harder  to  find  than  in  many  muscles  of  the  Invertebrates. 
Even  under  the  most  favourable  conditions,  e.g.  after  treatment 
with  gold  chloride,  which  stains  the  sarcoplasm  deep  red  or  black, 
while  the  fibrillar  substance  remains  uncoloured,  so  that  each  area 
of  Cohnheim  stands  out  distinctly,  no  further  differentiation  is 


I  ORGANISATION  AND  STRUCTURE  OF  MUSCLE  37 

visible  as  a  rule  within  the  latter,  even  with  the  most  powerful 
enlargement;  the  arese  appear  to  be  perfectly  homogeneous.  By 
the  use  of  proper  means  (alcohol,  acid),  which  facilitate  the  break- 
ing down  of  muscle-fibres  into  fibrils,  or  the  swelling  of  the  latter, 
it  becomes,  however,  possible  to  detect  the  fibrils  in  cross-section. 
Cohnheim's  areae  then  appear  to  be  subdivided  into  smaller  fields 
lying  in  close  juxtaposition  (Figs.  25,  h  ;  26,  B).  In  longitudinal 
section  also,  the  fibrillated  structure  of  the  muscle-columns — at 
least  in  places  —  becomes  distinctly  visible.  Still  it  must  be 
admitted  that  in  comparison  with  the  certainty  with  which  the 
muscle- columns  themselves  can  be  demonstrated,  their  composition 
as  bundles  of  fibrils  is  much  harder  to  determine. 

If  the  tyj)ical  muscles  of  Arthropods  already  exhibit  a 
superabundance  of  sarcoplasm  in  comparison  with  the  majority 
of  vertebrate  skeletal  muscles,  this  is  to  a  far  greater  extent  the 
case  with  the  a-typical  thorax  muscles  of  Insects,  As  compared 
with  the  first  type,  these  must  be  designated  "  dark "  muscles, 
which  is  the  more  legitimate,  since,  like  the  "  plasmic  "  muscle- 
cells  and  fibres  of  vertebrates  and  many  invertebrates,  they  are 
generally  distinguished  by  their  darker  colour  (reddish,  or 
brownish -yellow)  from  the  clear,  white  leg -muscles.  But  the 
most  typical  characteristic  of  these  wing-muscles  (thoracic  fibrils) 
of  insects  (discovered  by  Siebold,  and  first  described  minutely  by 
Kolliker)  is  their  readiness  to  separate  into  very  broad  fibrils 
(1  to  4  /u,),  which  are  bedded  in  the  cavities  of  the  copiously- 
developed  sarcoplasm.  The  sarcoplasm  again  is  richly  studded 
with  "  interstitial  granules " — which  are  often  excessively  large 
— and  arranged  in  regular  longitudinal  series  between  the 
fibrils. 

Further,  on  examining  fresh  preparations,  the  wealth  of 
trachese  is  very  striking.  They  not  only  wind  themselves  round 
the  bundles  of  fibrils  externally,  but,  as  appears  unmistakably  in 
transverse  section,  penetrate  inside  the  individual  fibres,  and 
ramify  freely  in  the  sarcoplasm.  Within  the  meshes  of  the 
network  of  trachete,  it  is  easy  in  cross-section  to  distinguish  a 
mosaic  of  circles,  corresponding  with  the  single  fibrils,  whose 
diameter,  as  compared  with  the  excessively  fine,  elementary  fibrils 
of  the  leg-muscles,  is  enormous. 

As  a  rule  there  is  no  sarcolemma  in  these  larger  bundles  of 
fibrils   (corresponding    to   muscle-fibres)    in    the   wing-muscles   of 


38  ELECTRO-PHYSIOLOGY  chap. 

insects ;  they  are  bounded  only  by  the  surrounding,  spongy,  con- 
necting-substance, and  supported  inside  by  the  system  of  branched 
tracheae.  The  tracheal  branches  thus  form,  as  it  were,  the 
skeleton  of  a  fibril  -  bundle,  while  the  sarcoplasm  fills  up  the 
cavities  that  remain  between  fibrils  and  tracheal  ramifications. 

Glancing  back  over  the  facts  that  relate  to  mass-disposition 
of  sarcoplasm,  vs.  contractile  substance  proper  of  the  fibrils,  the 
general  conclusion  seems  to  be  justified,  that  the  elements  of  those 
muscles  which  serve  the  most  2^^'>^sistent  or  most  strenvmis  action  are 
richest  in  sarcoijlasm.  (Cardiac  and  masticatory  muscles  of 
invertebrates  and  vertebrates,  float-muscles  of  Hippocampus  and 
other  fishes,  some  of  the  lateral  body-muscles  of  fishes,  especially 
those  in  the  tail  -  region,  which  govern  the  movements  of 
direction.) 

Knoll  (13,  p.  47)  pointed  out,  in  this  connection,  a  curious 
instance  of  divergence  in  the  tail-muscles  of  Torpedo  and  Eaja. 
In  the  former  there  is  a  well  -  developed  stripe  of  red,  dark 
muscle,  which  is  totally  absent  in  Raja ;  there  are  corresponding 
differences  in  the  swimming  movements  of  the  two  animals,  since 
in  Torpedo  the  flexible  tail  executes  a  series  of  rapid  sideway 
movements,  which  do  not  occur  with  Eaja. 

The  wing  -  muscles  of  birds  and  insects  afford  another 
example.  The  great  pectoral  muscle  of  the  best  fliers  consists 
exclusively,  or  almost  exclusively,  of  plasmic,  in  the  weak- winged 
"fowls"  predominantly  of  a-plasmic,  fibres.  In  the  guiding  muscles 
of  amphibia,  reptiles,  and  mammals  the  a-plasmic  and  plasmic 
fibres  are  intermingled ;  the  last  are  more  abundant  in  the  free, 
wild  species  of  mammals  than  in  the  domesticated  animals. 
In  the  rodents,  e.g.  (rabbit),  they  are  entirely  absent,  or  very 
sparsely  distributed,  in  certain  sections  of  the  leg-muscles.  In 
bats,  on  the  other  hand,  the  fibres  of  every  muscle  are  rich  in 
protoplasm. 

There  seems  therefore  to  be  a  direct  relation  hetiveen  the  ex- 
tension and  force  of  the  contractile  fibrils  and  the  hulk  of  surrotind- 
ing  sarcoplasm  (Knoll). 

If,  as  Sachs  conjectured,  the  nutrition  and  metabolism  of  the 
muscle-fibrils  {i.e.  of  the  contractile  substance)  are  intrinsically 
dependent  on  the  bulk  of  sarcoplasm,  this  relation  is  easy  to 
understand.  As  a  matter  of  fact  there  can  be  no  doubt  that 
energetic   chemical   changes  do  go   on   in   the   sarcoplasm,  as  is 


I  ORGANISATION  AND  STRUCTURE  OF  MUSCLE  39 

proved,  inter  alia,  by  the  frequent  appearance  of  fat -drops, 
which  are  presumably  in  close,  genetic  relation  with  the  inter- 
stitial granules  mentioned  above  (Knoll).  Again,  we  know 
that  certain  matters  which  penetrate  the  muscle-fibres  are  further 
distributed  to  the  sarcoplasm ;  e.g.  Leo  Gerlach  (21)  found  that 
the  muscle  -  fibres  of  frogs  which  had  been  treated  for  several 
days  with  indigo-carmine  became  speckled  with  blue,  particularly 
towards  the  tendon  end  of  the  fibres,  in  consequence  of  the  indigo 
assimilated,  and  often  exhibited  a  definite,  serial  arrangement  of  the 
pigment.  The  rows  of  blue  granules  lie,  like  the  fat- drops  in 
other  cases,  between  the  fibrils  in  the  sarcoplasm ;  so  that  the 
indigo-carmine  must  be  taken  up  by  the  sarcoplasm  in  solution. 
If,  then,  it  really  is  the  role  of  the  interfibrillar  plasma  to  preside 
over  the  nutrition  of  the  contractile  substance,  the  greater  abund- 
ance of  sarcoplasm  in  the  muscles  which,  serve  the  most  strenuous 
and  persistent  functions  is  readily  intelligible.  The  frequent 
pigmentation  of  the  dark,  "  plasmic  "  muscle-fibres  (as  previously 
cited)  seems  also  to  be  closely  related.  Such  are — in  opposition 
to  the  body-muscles — the  deep  purple-red  buccal  muscles  of  many 
snails  (Chiton,  Haliotis,  Limnseus,  Trochus,  Paludina,  Littorina, 
Patella),  the  cardiac  muscles  of  many  invertebrates  and  all 
vertebrates,  as  well  as  the  dark -red  muscles  which  contain 
haemoglobin. 

The  finer  structure  of  the  single  muscle-fihrils  {infra),  on  the 
other  hand,  seems  to  be  in  relation  with  quite  another  property 
of  the  muscular  elements,  i.e.  raijiclity  of  contraction.  We  have 
already  stated  that  distinct  cross-striation  of  the  fibrils  is  excep- 
tional in  the  uninuclear  cells  of  Invertebrates,  and  where  it 
does  appear  {e.g.  in  Medusae,  adductor  muscle  of  Pecten,  etc.) 
exists  only  in  the  more  swiftly  contracting  muscles.  Thus  0.  and 
E.  Hertwig  (22)  observed  that  the  individuals  of  the  Hydroid- 
colony  have  smooth  muscle-fibres,  so  long  as  they  remain  attached 
as  inert  hydroid  polyps  to  the  parent,  "  but  acquire  striated  fibrils 
directly  they  swim  off  as  active  Medusae."  Again,  the  tentacular 
muscles  of  the  Ctenophora  are  usually  smooth,  only  the  lateral 
muscles  of  Euplocamis,  which  contract  with  especial  vigour  and 
rapidity,  being  striated.  In  Vertebrates,  on  the  other  hand,  the 
bulk  of  the  muscles  is  composed  of  cross-striated  fibres,  and  only 
the  sluggishly  reacting  muscles  of  the  intestinal  tract,  urogenital 
apparatus,  and  blood-vessels,  are  smooth,  i.e.  exhibit  no  further 


40  ELECTRO-PHYSIOLOGY 


differentiation  in  their  fibrils.  Lastly,  in  the  Arthropoda,  which 
are,  generally  speaking,  characterised  by  extreme  rapidity  of 
movement,  all  the  muscles  are  striated,  and  it  is  just  among 
these  that  we  also  find  the  most  rapidly  contracting  fibres 
(thoracic  fibrils  of  insects). 

It  is  easy  to  demonstrate  that  the  cross-striation  of  a  muscle- 
cell,  or  fibre,  depends  on  the  cross-striation  of  the  single  fibrils. 
Each  of  these  appears .  in  longitudinal  section  as  though  it  were 
regularly  segmented,  or,  more  correctly,  built  up  of  separate 
layers,  which  exhibit  fundamental  differences  in  respect  of  optical 
properties,  and  affinity  for  staining,  as  indeed  of  all  chemical 
and  physical  reactions.  This  construction  is  most  evident  in 
the  thick,  thoracic  fibrils  of  insects,  and  in  the  bundles  of  fibrils 
known  as  ^'  muscle-columns,"  which,  in  consequence  of  the  regular 
juxtaposition  of  the  single — often  excessively  fine — fibrils  exhibit 
precisely  the  same  transverse  banding  as  that  which  we  ascribe 
in  this  instance  to  each  elementary  fibril.  The  optical  appearance 
of  the  striation  is  in  general  a  regular  succession,  of  light  and 
dark  bands,  which  lie  one  above  the  other  like  coins  in  a  rouleau. 
Such  a  series  of  stride  may  be  very  complicated  in  detail,  since  a 
whole  system  of  light  and  dark  parts  can  be  grouped  together, 
as  it  were,  in  a  higher  unit ;  the  regular,  periodical  alternation 
of  the  individual  segments  is,  however,  a  persistent  character- 
istic. The  separate  bands — as  will  be  shown  below — present 
quite  a  different  appearance  in  the  resting  and  in  the  contracted 
condition.  The  arrangement  in  the  resting  state  will  be  first 
considered. 

Both  in  Vertebrates  and  Invertebrates,  the  relaxed,  striated 
muscle-fibre,  or  bundle  of  fibrils,  exhibits  broad,  dark,  transverse 
bands  under  an  appropriate  power  of  the  microscope,  separated  again 
by  smaller,  clear  .bands ;  these  last,  in  suitable  preparations, 
can  at  once  be  recognised  as  the  expression  of  the  regularly  juxta- 
posed, homogeneous  segments  of  the  fibrils,  of  which  the  muscle- 
fibres,  or  muscle-columns,  consist  between  every  two  transverse 
planes  of  the  fibre.  In  the  simplest  cases,  each  dark  band 
appears  to  be  divided  in  the  middle  by  a  faint,  clear  line,  each 
light  band  by  a  dark  line  (Fig.  27,  /,  h  and  Z).  In  many  cases, 
however,  e.g.  in  the  Arthropod  muscles,  the  segmentation  is  much 
more  complex  (Fig.  27,  //  and  ///).  It  is  convenient,  with 
.  EoUett,  to  indicate  the  individual  segments  of  the  fibrils,  or  the 


ORGANISATION  AND  STRUCTURE  OF  MUSCLE 


41 


transverse  bands  or  stripes  to  which  these  give  rise  in  the 
entire  fibre,  by  a  system  of  letters.  The  large  sections  (Q),  which 
appear  dark  on  lowering  the  objective,  are  divided  by  the  band 
(Ii),  which  is  light  with  the  same  focus,  of  varying  breadth,  and 
not  usually  well  defined,  into  three  parts — the  two  "  dark 
bands "  (Querschichten),  and  the  less  strongly  refractive  Hensen's 
stripe  ("  Rensenclie  "  Mittelscheihe,  h),  which  is  not  always  visible. 
Schiefferdecker  gives  the  name  of  "  middle  band "  (Jf.  "  Mittel- 
schicM ")  to  a  very  fine  dark  line,  first  accurately  described  by 
Hensen,  which  sometimes  appears  in  the  "  middle  stripe "  (h), 
but  is  not  always  visible.     The  segments  (Q)  are  generally  longer 


/// 


Fig.  27. — Schema  of  the  transverse  striation  of  Beetle-mnscle.    (Rollett.) 


in  Arthropod  muscles  than  in  Vertebrates,  so  that,  with  the 
coincident  longitudinal  striation,  the  muscle-fibres  look  as  if  they 
were  composed  of  long,  dark  rows  of  granules  (Fig.  31).  The 
dark  band  which  bisects  the  clear  segment  with  a  low  objective 
(as  described  by  Amici)  is  known  as  Dobie's  line  (Z.  Zwischen- 
schicht,  Engelmann's  "  Ztvischenscheihe  ").  Krause  described  this 
band  as  the  "  transverse  line "  and  "  basal  membrane "  of  his 
"  muscle-cases  "  (infra).  Between  (Z)  and  the  two  clear  segments 
(tT),  which  in  the  simplest  case  (Fig.  27,  /)  are  only  sepa- 
rated by  it,  two  dark  bands  are  occasionally  visible  ;  they  are 
very  inconstant  in  their  appearance,  and  are  denoted  by  Eollett 


42  ELECTRO-PHYSIOLOGY 


as  (iV),  corresponding  with  Engelmann's  accessory  discs  ("  JSfchcn- 
scheiben")  (Schema  //,  Fig.  27). 

Finally  (Schema  ///),  the  dark  band  (N)  may  appear  in  the 
middle  of  the  clear  segment  (J),  so  that  Dobie's  line  (Z)  is 
bordered  directly  on  either  side  by  a  clear  line  (-£'),  followed 
by  (iV),  and  then  by  another  clear  line  (J),  so  that  the  entire 
system  of  bands  in  a  fibre-segment  enclosed  between  two  Dobie's 
lines  (Z)  is  as  follows  : — {ZENJQJNEZ)  ;  the  next  simplest 
case  is  (ZJYJ  Q  J  JYZ);  the  simplest  of  all  (Z  J  Q  J Z).  It 
is  important  to  remember  that  none  of  these  several  systems  of 
strise  can  be  regarded  as  characteristic  of  all  muscle-fibres  in  any 
particular  species  of  animal.  On  the  contrary,  the  three  conditions 
of  striation  indicated  in  the  figures  may  occur  in  one  and  the  somie 
fibre,  and  merge  into  one  another,  as  shown  by  Engelmann  in  the 
muscles  of  insects  in  particular.  This  effect  is  due  in  the  first 
place  to  different  conditions  of  contraction  in  the  fibres ;  the  most 
complicated  kind  of  cross-striation  always  corresponding  with  the 
greatest  relaxation  of  fibre.  This  by  no  means  excludes  the  possi- 
bility of  specific  varieties  of  striation ;  all  the  observations  tend 
to  show  that  if  it  were  possible  to  investigate  the  muscle-fibres 
of  different  animals,  or  the  different  muscle-fibres  of  the  same 
animal,  when  perfectly  relaxed,  or  at  the  same  degree  of  exten- 
sion, they  would  present  very  different  appearances. 

The  reaction  of  striated  muscle-fibres,  or  individual  layers  of 
fibrils,  and  of  the  sarcoplasm,  to  different  reagents,  is  extremely 
interesting  both  morphologically  and  physiologically, — the  differ- 
ences exhibited  being  no  less  striking  than  in  regard  to  optical 
properties.  This  is  plainly  expressed  by  the  different  colorability 
of  the  individual  segments.  If  the  transverse  section,  or  the 
entire  muscle -fibre,  is  appropriately  treated  with  hematoxylin, 
we  find  that  only  the  contractile,  fibrillated  substance  of  the 
muscle-columns  stains  in  the  first  case,  and  not  the  interstitial 
sarcoplasm.  On  comparing  good  hsematoxylin  preparations  of 
muscle-fibres  in  longitudinal  section,  it  is  evident  that  only  the 
segments  (Q),  (N),  and  (Z)  are  stained,  while  the  intermediate  spaces 
between  them  (i.e.  the  sarcoplasm)  and  the  strise  (h),  (J),  and  (U) 
are  almost  or  wholly  unstained. 

It  has  been  shown  that  the  gold  chloride  method  imder  certain 
conditions  gives  an  opposite  reaction ;  the  sarcoplasm  only  stains, 
while  the  contractile  fibrils  embedded  in  it  remain  uncoloured. 


I  ,  ORGANISATION  AND  STRUCTURE  OF  MUSCLE  43 

Hence  in  cross-section  (Bieclermann,  Thin,  Gerlach,  Eetzius,  and 
others),  Cohnheim's  arete  stand  out  colourless  from  the  very- 
distinct  red  plexus  of  the  sarcoplasm.  The  longitudinal  section 
of  fibres  treated  with  gold  is  no  less  divergent.  Gerlach,  who 
investigated  vertebrate  muscle  only,  characterises  it  as  "  speckled  " ; 
each  fibre  appears  interspersed  throughout  its  thickness  with  a 
crowd  of  dark,  red  or  black,  dots  and  streaks,  which,  as  Gerlach 
correctly  observed,  give  an  impression  of  continuous  and  often 
varicose  fibres  in  places,  and  are  only  too  easily  mistaken  for  fine 
nerve-fibrils  (Fig.  28).  The  gold  chloride  figures  of  Arthropod 
muscles  are  generally  much  more  regular,  r^  i 

and  accordingly  present  less  ambiguous        /'{'•i         '     '|i 
conclusions.  //  /*  ,     1 1 

Before  discussing  these  facts,  it  is     (  ,'    <        ;  ( '    "     \  J  ,4 
advisable  to  consider  briefly  the  simple    \\*'    'i,>^,,'  ; '    '    j  ,|,    ,'/ 
action   of    acids,   since    this    is    always     \v       \        i  'j'    \\  uj 
combined  with  the  gold  method.      The       '     i     '  !!  •'' 

first  effect  of  treatment  with  very  weak  ',|  ,. 

acids  (acetic,  formic,  haloid,  etc.)  is  best       jj.  ,  ^        ' '  lu\ 

exhibited  in  muscle-fibres  which  have        !  1  '         i 

lain    in    strong    alcohol    (93    °/o)    ^^^       ''    '        '  *      V 

twenty-four   hours.       The   earliest   and      /  '  f 

most  striking;  changes  occur  within  the    '  ',  I 

system  of  stria3  (Q  h  Q),  which  swell  |; 

up,  and   seem   to    bulge  out   from   the  '   w' 

wall  of   the  fibre  (or  muscle -column). 

rT^^  •  f  i  FiG.    28. — Surface    of    muscle  -  fibre 

This  process  may  go  so  far,  on  apply-  (p^og)  treated  Avith  gold  cworide 
ing  a  somewhat  stronger  solution,  as  to     *"  ^^°^^  oeriacii's  "  speckles." 

°  .  .  .  .  (Biedennann.) 

effect    radical    alteration    in   the   strife 

(JV  Z),  which  lie,  as  it  were,  crushed  in  between  the  much- 
broadened  and  now  homogeneous  {Q)  bands  (Fig.  29). 

On  the  other  hand,  the  rapid  swelling  of  the  segments  {Q  h  Q) 
at  a  still  more  advanced  stage  of  the  acid  reaction  may  produce 
an  explosive  disintegration  of  the  muscle-fibres  into  discs,  by  a 
process  of  continuous  splitting  up  within  (Q),  by  which  the 
segments  {JN E,  Z,  E  NJ)  are  finally  driven  apart,  and  isolated 
as  discs.  It  would  follow  that  the  changes  which  the  longitudinal 
section  of  the  muscle-fibre  undergoes  during  the  action  of  strong 
acids  are  to  be  referred  partly  to  changes  of  form  in  the  muscle- 
columns  (or  fibrils),  due  to  differences  of  turgescence  in  the  indi- 


44  ELECTRO-PHYSIOLOGY 


vicinal  segments  of  the  fibril,  accompanied  by  changes  of  refracti- 
bility ;  partly,  however,  to  the  sarcoplasm,  which  also  nndergoes 
changes  both  in  respect  of  local  distribution  and  of  refractibility. 
Since  the  individual  segments  of  the  fibrils,  or  muscle-columns, 
swell  in  different  degrees,  so  that  each  element  appears  alter- 
nately thickened  and  constricted  (a  form  frequently  observed  by 
EoUett  in  fresh,  spontaneously  contracting  muscle-fibres),  it  is 
evident  that  the  sarcoplasm  which  separates  the  muscle-columns 
.„„.._  ^'-^'~^.         must  be  partially  driven  out  of  the 

-  ^^_  _  interstitial    spaces    of    the    swollen 

'^'' '''''i^ii'ilu^Mmmfiin^^^       i        scctions,  whilc  it  accumulates  in  the 
^    interstices  of  the  narrowed  sections. 
"^^^^'nllSm^      '^   Eemembering  further  that  the  sub- 
•',t  ^    stance  of  the  fibrils  (muscle-columns) 

'  ..,       '-::::;  -  iv   is  clear  in  acid,  swollen  muscle,  while 

,'  W'l         the  sarcoplasm  is    dark  (as  in    the 

iij/!i.mm    ""^/  iim    "  normal  fibre  with  a  high  adjustment), 

the  explanation  of  the  acid  reaction 
SiifiTiiii  iiimi  (iijiiiinrlfij  IS  very  simple. 

I  The  acid  figures  described  corre- 

^ , ,  .  i'  spond   (as     EoUett    shows)    in    all 

essential  points  with  the  gold  chlo- 

"''''^iilii'Hiif'ii'iiiim.i'iTJi  ride  figures,  except  that  in  the  latter 

^  the  darker  knots  of  sarcoplasm,  as 

iU       ,  1..11' "'  'l','  ,'.mV.'l!!l  well  as  the  connecting  lines,  which 

u^""'  result  from  the  impregnation  of  the 

Fig  29-Muscie-flbreof^p;.ocii«s™/j.es  ^^y^^^\     ^rc   morc   or   Icss   intensely 

(alcohol)  splitting  into  discs  after  treat-  '  '' 

nient  with  weak  acid ;   swelling  of  (C)    Colourcd,    whilc    the    fibrillatcd    Sub- 

ayers.   (  o  e  .)  stauce    is    unstaincd,   so    that    the 

longitudinal  section  of  the  fibre  gains  considerably  in  clearness 
and  precision. 

Another  kind  of  discoid  disintegration  (differing  essentially 
from  the  above)  was  first  described  by  Bowman,  and  has  recently 
been  reinvestigated  by  Eollett,  in  the  muscles  of  insects.  This 
is  a  peculiar  action  of  strong  alcohol  (93  %),  in  which  the 
muscles  have  been  steeped  for  some  time  (twenty-four  hours  to 
fourteen  days).  The  figures  obtained  under  these  conditions  are 
very  characteristic  (Fig.  30). 

In  fibres  where  the  cross-striation  corresponds  with  the  simplest 
schema  {Z  J  QhQJ Z),  the  segments  (Q  h  Q)  are  found  as  trans- 


ORGANISATION  AND  STRUCTURE  OF  MUSCLE 


45 


verse  discs,  which  are  either  completely  isolated,  or  still  lie  within 
the  sarcoplasm ;  this  last  is  more  or  less  swollen,  and  divided  by 
delicate  partition  walls,  corresponding  with  the  segment  (Z),  into 
solitary  cases  or  compartments  arranged  in  longitudinal  series, 
each  case  containing  a  transverse  disc,  corresponding  elsewhere 
with  the  system  of  stride  {NJQh  Q  J N).  It  is  to  be  noted  that 
the  segments  (QJiQ)  do  not  swell  out  as  in  the  acid  reaction, 
but  are  only  separated  by  alterations  within  the  segment  (Z). 
The  sarcoplasm  appears  to  be  constricted  at  the  junction  of  the 
partition  walls,  while  the  cases  between  bulge  outwards. 

Bowman  explains  this  bulging,  which 
is  visible  before  the  final  breakdown  into 
discs,  by  the  withdrawal  of  the  sarcolemma 
from  the  surface  of  the  discs,  to  which  it 
adheres  firmly. 

EoUett,  on  the  contrary,  observes  with 
justice  that  it  is  not  merely  the  sarcolemma 
that  shrinks,  but  also  a  portion  of  the  sarco- 
plasm, which  covers  the  inner  side  of  the 
sarcolemma  in  a  sheet  of  varying  thick- 
ness,  so    that   we    are   dealing 


II  ill" ' 

iiijji.i};' 


•\ 


,h .!' 


'-a. 


% 


Fig.  30. —Muscle- 
fibre  of  Opatrvni 
sahulosiim  broken 
down  into  discs 
(alcoliol  treat- 
ment).   (Rollett.) 


with  a  local  vacuolation  of  the 
muscle  substance. 

Our  own  experiments  lead 
us  to  accept  EoUett's  explana-  y^y,,  --^^ 
tion  of  the   alcohol  disintegra-       \^Jv  '''^ 
tion     into     discs     as     entirely  ''S^ 

satisfactory.      He  assumes  that  -^ 

the  endosmotic  pressure  of  the  fluid  in  the  circular  canals 
originally  present  in  the  muscle  increases  considerably,  but 
that  the  segment  (Z)  possesses  a  certain  firmness  and  resist- 
ance, while  the  impinging  layer  (U)  or  (J)  is  very  yielding, 
and  therefore  liable  to  maceration  from  the  fluid.  This  results 
in  the  freeing  of  the  intermediate  layers  as  a  disc  within  a 
compartment,  the  walls  of  which  are  formed  above  and  below 
by  a  segment  (Z),  at  the  sides  by  the  bulging  of  the  primitive 
canal.  The  peculiar  resistance  of  the  segment  (Z)  had  already 
been  discovered  by  Engelmann. 

The  figures  which  arise  from   this  discoid  disintegration  of 
the  muscle-fibres  might,  of  course,  be  interpreted  on  the  theory 


46  ELECTRO-PHYSIOLOGY 


of  W.  Krause,  that  every  muscle-column  i.s  composed  of  strata  of 
"  muscle- cases/'  which  in  juxtaposition  form  the  "  muscle-com- 
partments "  of  the  entire  fibre ;  each  muscle-case,  bounded  beneath 
by  {Z)  the  '•'  basal  membrane,"  contains,  as  well  as  fluid  corre- 
sponding with  (J),  a  "  muscle-prism,"  represented  like  the  Bowman 
"  discs  "  by  the  {Qh  Q)  system  of  strife.  Krause  only  takes  account 
of  the  fibrillated  structure  of  the  muscle-fibres,  in  so  far  as  he 
assumes  the  muscle-prism  to  consist  of  muscle-rods  (Bowman's 
"  sarcous  elements  "),  which,  according  to  the  description  given 
above,  correspond  with  the  segments  of  fibrils  {Q  h  Q)  only.  The 
untenability  of  this  theory,  according  to  which  not  fibrils,  but 
muscle-cases,  are  the  elementary  constituents  of  the  muscle-fibre, 
is  obvious  from  the  facts  we  have  stated ;  the  breakdown  into  discs 
within  the  segment  {Q)  in  the  acid  reaction  is  very  convincing 
evidence  against  it.  Nor  is  there  any  better  justification  for  the 
muscle-elements  of  Merkel,  which  are  each  bounded  by  two  {Z),  in 
this  case  necessarily  assumed  to  be  divisible.  This  is  not  the  place 
to  enter  into  the  many  other  systems  (including  Blitschli's  "  cell 
theory  ")  that  have  been  elaborated  from  time  to  time,  in  regard 
to  the  much  disputed  finer,  and  finest,  structures  of  striated 
muscles. 

We  have  already  had  frequent  occasion  to  refer  to  the  oiMcal 
'pro'parties  of  muscle-fibrils,  especially  in  striated  muscle.  Even 
when  examined  in  ordinary  light  the  different  segments  of  the 
striated  fibrils  exhibit  a  very  different  refractibility ;  it  may 
indeed  be  said,  with  reference  to  Eollett's  system  of  indicating 
the  individual  segments,  that  all  the  bands  denoted  by  consonants 
are  more  highly  refracting,  and  also  doubly  refracting  {cmisotTo-pous) 
although  in  very  different  proportions. 

As  was  said  above,  the  bands  {Z)  and  (iV)  appear  much 
darker  than  (§)  with  a  certain  (low)  power  of  the  microscope, 
and  it  is  owing  to  the  strong  refractibility  of  {Z')  in  particular 
that  it  is  easily  recognised  even  in  imperfect  preparations.  The 
stripe  denoted  by  the  vowels  (/)  and  {E),  as  well  as  (/i),  are,  on 
the  other  hand,  less  refractile  and  singly-refracting  {isotroijous) ; 
these,  under  conditions  which  make  the  bands  denoted  by  con- 
sonants appear  dim,  will  be  clear  and  inverted.  The  doubly- 
refracting  property  of  striated  muscle-fibres  was  discovered  by 
Beck  in  1839,  but  Briicke  in  1857  was  the  first  to  examine  it 
minutely. 


I  OKGANISATION  AND  STRUCTURE  OF  MUSCLE  47 

Under  a  polarising  microscope,  with  crossed  Nicol  prisms,  the 
anisotropous  bands  {Z N)  and  (Q),  which  look  dark  in  ordinary 
light,  with  a  low  objective,  appear  clear  and  shining,  standing 
out  sharply  in  a  dark  field,  while  the  isotropous  bands  {J E)  and 
(A)  remain  dark  under  the  same  conditions.  Very  beautiful 
figures  are  exhibited  by  muscle-fibres  in  polarised  light  when  the 
field  of  vision  is  coloured  by  a  mica  or  gypsum  plate  of  corre- 
sponding diameter.  The  anisotropous  layers  stand  out  vividly 
in  the  complementary  colours,  according  to  the  direction  of  the 
fibres.  Light  falling  parallel  with  the  long  axis  of  the  fibrils  is 
singly  refracted.  With  crossed  prisms  a  transverse  section,  if 
sufficiently  vertical  to  the  fibre  axis,  remains  dark  in  all  its  parts 
and  at  all  azimuths,  and  does  not  change  colour  anywhere  with  a 
gypsum  background. 

The  anisotropous  portions  are  also  uniaxial.  Briicke  ascer- 
tained that  they  were  positive  by  means  of  a  movable  quartz  wedge  ; 
each  muscle-fibre  acts  like  the  thick  end  of  a  quartz  wedge  when 
lying  parallel  to  its  axis,  and  is  therefore  positive  like  quartz. 

EoUett  has  recently  applied  the  spectrum  analysis  of 
polarised  light  to  this  investigation,  and  has  confirmed,  with  the 
"  spectro-polarisator,"  the  earlier  observations  of  Engelmann,  viz. 
that  {Z)  and  {N)  are  less  positively  doubly-refracting  than  the  less 
refractile  segment  (Q).  At  the  same  time  the  remarkably  clear 
and  sharp  figures  obtained  with  this  method  leave  no  doubt 
that  the  accessory  discs  {N)  are  just  as  much  due  to  doubly 
refracting  segments  of  the  fibrils  as  {Q)  or  {Z).  All  the  inter- 
communications of  sarcoplasm,  on  the  other  hand,  look  quite  dark 
polarised  light,  so  that  the  doubly-refracting  segments  of  the 
muscle-columns  in  the  longitudinal  section  of  the  fibre  "  lie  com- 
pletely isolated  on  a  dark  field  in  regular  series  close  to  one 
another." 

Engelmann  (2)  has  remarked  that  double  refractibility  is  a 
widely  distributed  property  of  contractile  protoplasm,  appearing 
even  among  protozoans.  The  stalk  muscle  of  Vorticella,  e.g., 
exhibits  strong  double  refraction,  and  the  fibrils  behave  exactly 
like  the  fibrils  of  striated  muscle,  i.e.  are  uniaxial,  with  the  axis 
parallel  to  the  longitudinal  direction  of  the  fibres.  In  Stentor, 
the  cortical  layer  of  plasma  is  usually  doubly-refracting  through- 
out its  diameter,  as  well  as  the  muscle-fibrils ;  double  refracti- 
bility is  also  very  conspicuous  in  the  rays  of  Actinospherium, 


ELECTRO-PHYSIOLOGY 


where  each  plasma  ray  acts  like  a  doubly-refracting  fibre  with 
one  optical  axis,  which  is  parallel  to  the  longitudinal  direction 
of  the  fibre,  and  therefore,  generally  speaking,  with  the  direction  of 
contraction  in  the  plasma.  The  same  properties  also  characterise 
the  fibrils  of  the  epithelial  muscles  of  Hydra.  The  behaviour 
of  the  bi-obliquely  striated  muscle-cells  of  many  vertebrates  in 
polarised  light  is  also  remarkable.  According  to  Engelmann, 
e.g.,  "  the  optical  axis  of  the  fibrils  does  not  coincide,  as  might  be 
expected  from  analogy,  with  their  longitudinal  direction,  but  in- 
variably with  the  long  axis  of  the  muscle-fibres  " :  the  latter,  no 
matter  what  angle  the  fibrils  form  with  the  fibre-axis,  are  always 
at  maximum  clearness,  provided  the  axis  lies  at  an  angle  of  45° 
to  the  plane  of  polarisation  between  the  crossed  Mcol  prisms. 

Double  refractibility  therefore  appears  as  a  characteristic 
property  wherever  the  contractile  particles  of  plasma  lie  perma- 
nently in  a  definite  direction,  and  moreover  seems  invariably  to 
denote  uniaxial  particles,  whose  optic  axis  coincides  with  the  direct 
tion  of  contraction.  The  striated  fibrils  must,  with  Engelmann,  be 
regarded  as  consisting  mainly  of  an  isotropous  basal  substance, 
running  longitudinally,  in  which  the  doubly-refracting  particles 
(which  must  be  regarded  as  the  seat  of  the  contracting  forces) 
are  arranged  in  regular  striae,  corresponding  with  the  metabolous 
segments. 

It  remains  to  give  a  brief  account  of  the  changes  in  cross- 
striation  which  take  place  during  the  contraction  of  the  muscle- 
fibre,  since  they  are  of  almost  equal  morphological  and  physio- 
logical interest.  As  we  learn  by  observation,  the  changes  of  form 
in  fibre,  or  fibril,  of  the  muscle  are  a  shortening  and  a  thickening  ; 
and  this  of  course  not  merely  in  the  entire  fibril,  but  in  each 
individual  tract  of  the  same,  and  each  individual  segment. 

If  the  attention  is  fixed  on  a  contracted  spot  in  a  living 
fibre,  e.g.  in  insect  muscle,  which  frequently  exhibits  short  waves 
of  contraction,  with  relatively  low  velocity,  long  after  preparation, 
it  is  easy  to  distinguish  two  kinds  of  transverse  bands  within  the 
wave ;  one  small  and  invariably  dark,  the  other  clear  and  some- 
what broader.  The  contracted  fibres  therefore  present  on  the 
whole  an  aspect  similar  to  the  resting  fibres,  i.e.  a  regular 
alternation  of  dark  and  light  cross -bands,  only  the  single  strife 
are  much  closer  together,  the  dark  bands  much  smaller  than  in 
the  relaxed  fibre. 


ORGANISATION  AND  STRUCTURE  OF  MUSCLE 


49 


It  is  also  easy  to  see  that  the  dark,  sharply  defined 
bands  appear  where  the  relaxed  muscle  presents  the  segments, 
{JZJ),  or  {J NE,Z,E  N  J),  and  that  the  light  bands  correspond 
essentially  with  the  contracted  strife  (^  A  Q). 

The  muscle-fibres  of  insects,  killed  by  strong  alcohol,  often 
exhibit  local  contractions  ("  fixed  waves  of  contraction  ")  in  which 
the  histological  changes  pro- 
duced in  the  striated  fibrils 
during  the  transition  from  rest 
to  contraction  can  be  ascer- 
tained exactly  by  means  of 
staining  methods  and  reagents. 
These  very  subtle  manifestations 
are  of  the  greatest  theoretical 
interest,  and  must  be  discussed 
a  little  more  fully. 

As  before,  we  may  accept 
the  penetrating  conclusions  of 
EoUett  (22).  On  examining  a 
well-fixed  wave  of  contraction, 
from  a  fibre  of  Otiorhynchus 
Tnastix  stained  with  hsematoxy- 
lin  (Fig.  31),  it  is  in  the  first 
place  evident  that  the  dark-blue 
band  (C)  of  the  contracted  por- 
tion of  the  fibre,  Nasse's  "  con- 
traction-disc," is  derived  from 
the  transformation  of  the  system 
{JNE,Z,ENJ),  and  is  there- 
fore the  same  section  which 
Engelmann  denotes  as  isotropous, 
and  EoUett  as  the  arimetabolous 
layer  (a). 


«^  w- f^  w  ..^  p^  *^  ^t^,^^^ 


»i«i 

i&&i 


Fig.   31. — Muscle -tibre  of  Otiorhynchus  mastix, 
showing  wave  of  contraction.    (Rollett.) 


In  the  relaxed  arimetabolous  layers  the  bands  (Z)  and  (iV)  are 
deeply  stained,  the  bands  (E)  and  (J)  not  at  all,  or  very  slightly ; 
in  the  relaxed  "  metabolous "  sections  (Q  h  Q)  (Engelmann's 
"  anisotropous  "  layer),  which  Rollett  denotes  by  ytt,  the  ends  of 
Q  are  more  deeply  stained  than  the  centre  h  (Hensen's  stripe). 
With  increasing  contraction  of  the  section  (a),  the  diminishing 
bands   {N)  draw  nearer  and  nearer  to  {Z),  until  at  last  the  two 

E 


50  ELECTRO-PHYSIOLOGY 


{E)  lines  between  {N)  and  {Z)  can  no  longer  be  distinguished,  as 
is  the  case  at  the  outset  in  the  less  richly  striated  fibres.  A 
striking  change  occurs  in  the  next  stage  within  the  (a)  system. 
Instead  of  the  colourless  segment  (J)  two  strongly-coloured  bands 
appear,  while  a  clear  stripe  takes  the  place  of  {Z)  between  them. 
Eollett  denotes  the  former  by  (/''),  and  the  latter  by  {Z'),  since 
they  are  undoubtedly  derived  from  (J)  and  {Z),  as  appears  particu- 
larly from  their  behaviour  in  polarised  light — the  dark  (/')  like 
the  light  (J)  is  singly  refracting,  while  the  clear  {Z')  like  {Z)  is 
doubly  refractile.  When,  as  sometimes  happens  before  the 
last  stage  is  completed,  the  segments  {J')  are  not  yet  quite  dark, 
the  segments  {Z')  on.  the  other  hand  not  quite  light,  so  that 
they  resemble  each  other,  the  muscle-fibres  meeting  at  the  points 
of  the  contraction  wave  exhibit  most  indistinct  cross-striation ; 
this  is  the  so-called  homogeneous  stage  of  earlier  authors,  form- 
ing the  transition  to  the  system  (J')  and  (Z'  -\-  J'),  which  again 
represents  the  commonest  transition  to  the  series  of  bands  in  the 
completely  contracted  muscle.  While  the  clear  (Z^)  is  disappear- 
ing between  the  dark  (J'),  these  in  their  turn  melt  into  the 
"  contraction-band  ''  {(T),  as  described  by  Nasse,  which  is  highly  re- 
fracting, very  dark,  and  intensely  blue,  in  the  hsematoxylin 
reaction.  It  obviously  corresponds  with  the  system  (J-\-Z-\-J) 
or  (J-ir  N -\-  U  -\-  Z  -{-  E  +  jV -\-  J)  of  the  relaxed  and  resting  fibres, 
from  the  transformation  of  which  it  has  arisen. 

The  changes  within  the  (metabolous)  segments  {Qh  Q)  are 
at  first  less  striking,  and  the  contraction  is  also  smaller.  Later  on 
the  band  clears  up,  the  difference  between  the  darker  (Q)  and  (h) 
grows  less  and  less,  and  finally  a  dark,  ill-defined  band  {m.  Eollett) 
appears  in  place  of  the  latter.  Eollett  denotes  the  entire  series 
of  altered  segments  {Q  h  Q)  in  the  contracted  fibre  by  {Q').  The 
transition  from  relaxation  to  contraction  in  a  fibre  often  proceeds 
much  more  slowly  than  in  the  example  described  above ;  the 
single  stages  may  extend  over  several  segments  of  the  fibres,  an 
effect  which  only  enhances  the  clearness  of  these  figures. 

Polarisation  phenomena  during  contraction  are  not  easy 
to  follow  on  fresh  muscle-fibre,  but  Eollett  (22)  was  able  to 
assure  himself  of  a  diminution  of  the  double  refractibility, 
a  fact  that  can  also  be  ascertained  from  fixed  waves  of  con- 
traction, and  had  been  previously  conjectured  by  Engelmann  (23) 
(cf.  Ebner,  24,  p.   233).     It  is  directly  apparent  from  the  fact 


ORGANISATION  AND  STRUCTURE  OF  MUSCLE 


51 


a 


that  muscle-fibres  exhibiting  such  fixed  waves  of  contraction, 
when  considered  on  a  gypsum  ground  in  the  plus  and  minus 
condition,  exhibit  no  particular  alteration  of  colour  in  the  con- 
tracted as  compared  with  the  relaxed  parts,  although  normally 
increase  of  bulk  in  a  muscle-layer  does  perceptibly  deepen  the 
colour,  e.g.  when  two  relaxed  fibres  partially  cover  each  other. 
Even  high  waves  of  contraction  exhibit,  in  comparison  with 
the  relaxed  portions  of  the  fibre,  little  or  no  alteration  qua  increase 
or  decrease  of  colour,  in  the  ascending  or  descending  stages. 

This   leads  us   to  infer   that  in   contracted  muscle-fibres  the 
increase  of  colour  which  should  go  along  with 
the  thickening  of  the  fibre  is  compensated,  or 
over :  compensated,    by    a    diminution    of    the  •{ 
double    refraction    coincident    with    the    con-  | 
traction.  ^ 

The  method  of  polarised  light  enables  us 
further  to  form  a  conclusion  with  regard  to 
another  important  point  in  the  behaviour  of 
striated  muscle-fibres  during  contraction.  If 
the  height  of  the  metabolous  and  arimetabolous 
segments  is  compared  in  an  appropriate  pre- 
paration (Fig.  32)  with  crossed  prisms,  during 
the  transition  from  the  relaxed  to  the  contracted 
portions  of  the  fibre,  it  may  be  seen  that  with 
increasing  contraction  the  height  of  the  iso- 
tropous  (arimetabolous)  segments  diminishes 
more  than  that  of  the  anisotropous  (metabol- 
ous), so  that  the  volume  of  the  latter  increases 
at  the  expense  of  the  former,  the  total  volume 
of  the  section  in  question,  like  that  of  the  entire 
fibre,  remaining  constant.  Engelmann  has  established  these  facts 
in  appropriate  objects  by  micrometric  measurements.  In  order  to 
explain  the  effect  he  assumes  that  fluid  passes  from  the  isotropous 
to  the  anisotropous  substance  in  contraction ;  the  anisotropous 
substance  swells,  the  isotropous  shrinks.  This  water-exchange 
between  the  metabolous  and  arimetabolous  segments  must  natur- 
ally be  imagined  as  between  the  elements  of  the  muscle-column,  or 
single  fibril,  corresponding  with  these  segments.  An  inverse 
change  in  volume  occurs  upon  relaxation,  and  the  surplus  of  fluid 
returns  to  the  isotropous  (arimetabolous)  system.      This  theory  is 


a\ 

Mr— ■ 

■ 

^^^^^^^^^M 

A* 

«/ 

/     H-i 

/'      \\ 

1                           ■ 

■■■ 

Fig.  32. — Muscle-fibres  of 
Tele'phoriis  during  con- 
traction, a,  In  ordin- 
ary ;  &,  in  polarised 
light.  (Engelmann. 
Prom  Foster's  Text-Book 
of  Physiology.) 


52  ELECTRO-PHYSIOLOGY 


not  only  supported  by  the  changes  in  volume  {supra)  of  the  two 
chief  systems  of  segments  in  each  fibril,  but  is  also  confirmed  by 
the  diminution  of  double  refractibility  already  mentioned  in  con- 
traction, as  well  as  by  the  fact  that  under  these  conditions  the 
isotropous  (arimetabolous)  bands  appear  darker  and  less  trans- 
parent. The  anisotropous,  on  the  contrary  (with  the  exception 
of  the  middle  disc),  is  clearer  and  more  transparent  in  ordinary 
light.  In  proportion  as  the  segments  {Q)  (dark  bands)  imbibe 
water  from  the  isotropous  system,  they  must  become  not  only 
more  voluminous,  but  also  less  refractile,  and  clearer,  as  well  as 
less  doubly-refracting.  The  isotropous  bands,  on  the  other  hand, 
would  become  smaller  and  more  refractile,  and  darker  in  appear- 
ance, as  is  actually  the  case.  Finally,  the  alterations  in  colour 
of  the  contracted  section  of  the  fibre  agree  well  with  the  theory 
that  the  anisotropous  segments  swell  at  the  expense  of  the 
isotropous.  The  colourability  of  turgescent  bodies,  as  well  as 
their  chemical  constitution,  is  known  to  depend  in  great  measure 
upon  the  degree  of  turgor  at  the  moment.  The  rule  for  each 
single,  turgescent,  colourable  mass  is  that  it  stains  the  more 
intensely  in  proportion  as  it  contains  less  water  of  imbibition. 
As  a  matter  of  fact,  increased  colourability  of  the  arimetabolous 
(isotropous)  bands  can  be  observed  during  contraction,  while  the 
metabolous  (anisotropous)  segments  stain  much  less  deeply  with 
hsematoxylin  than  during  the  resting  state. 


BiBLIOGEAPHY 

1.  Ballowitz.     FibrillJire  Structiir  iind  Contractilitiit.      Pfliiger's  Arch.  46  Bd. 

p.  433. 

2.  Engelmann.     Pfliiger's  Arch.   11  Bd.     Ueber   Contractilitiit  und  Doppelbre- 

chmigs  Vermogen.     1875. 

3.  BuTSCHLi.   Bronn's  Klassen  und  Ordnungen  der  Thiere  (Protozoa  IL ) 

4.  M.  Verwokn.     Psychophysiologische  Protistenstudien.     Jena  1889. 

5.  CzERMAK.    Zeitsclir.  f.  wiss.  Zool.     IV.     1853. 

6.  KiJHNE.     Zeitschr.  f.  Biologie.     N.  F.  23.     1886.     p.  93  ff. 
y    y..  /  Reichert's  Archiv.     1859.     p.  824. 

I  Myologisclie  Untersuchiingen.     Leipzig  1860.     p.  23. 

8.  Rhode.    Die  Muskulatur  der  Chaetopoden  (Zoolog.  Beitrage  von  A.  Schneider.  I.) 

9.  0.  und  R.  Hertwig.     Jenaische  Zeitschr.  f.  Naturwiss.      XV.     1881.     p.  1  if. 

10.  E.  Balloavitz.     Arcliiv  f.  mikrosk.  Anatomic.     39  Bd.     p.  291  ff. 

11.  G.  ScHWALBE.     Archiv  f.  mikrosk.  Anatomie.     5  Bd.     1869. 

12.  Engelmann.     Pfliiger's  Arch.     25  Bd.     1881.     (Ueber  den  faserigen  Bau  der 

contractilen  Substanzen  u.  s.  w. ) 


I  ORGANISATION  AND  STRUCTURE  OF  MUSCLE  53 

13.  Knoll.     Denkschriften  der  math.  -  naturwiss.  Klasse  der   kais.   Akademie  der 

Wiss.  in  Wien.     LVIII.     1891.     p.  634. 

14.  H.  FoL.     Compt.  rend.     Tom.  106.    p.  306.     1888. 

15.  Steinach.    Pfliiger's  Arch.     52  Bd.     1892. 

16.  Heidenhain.     Studien  des  physiolog.  Instituts  zu  Breslau.     Heft  I.     1861. 

17.  Deasche.     Yerhandl.  der  anatom.  Ges.     1892.     p.  250. 

18.  Knoll.     Sitzungsber.  der  Wiener  Akademie.     CI.     Ahth.  III.     1892.     p.  498. 

19.  Retzius.    Biolog.  Untersuchungen.     1881. 

20.  RoLLETT.    Untersuchungen  iiber  den  Bau  der  quergestr.  Muskelfasern.    I.  und  II. 

Aus  den  Denkschr.  d.    mathem. -naturwiss.    Klasse  der   Wiener   Akademie. 
XLIX.  und  LI.    1885. 

21.  Leo   Geelach.    Ueber  das  Verhalten   des   indigoschwefelsauren    Natrons    im 

Knorpelgewebe  lebender  Thiere.     Habilitationsschrift.     1876. 

22.  RoLLETT.    Denkschriften  der  Wiener  Akademie.     LVIII.     1891.     (Unters.  iiber 

Contraction  und  Doppelbrechung  der  quergestr.  Muskelfasern.) 

23.  ENGELMA.NN.    Piiliger's  Arch.     VII.     p.  174. 

24.  V.  V.  Ebnee.    Untersuchungen  iiber  die  Ursache  der  Anisotropic  organ.  Sub- 

stanzen.     Leipzig  1882. 

25.  J.  B.  Haycraft.    On  the  Minute  Structure  of  Striped  Muscle.     Pro.  Roy.  Soc. 

Vol.  XLIX.     1891. 


CHAPTEE  II 

CHANGE    OF    FORM    IN    MUSCLE    DURING    ACTIVITY 

Some  of  the  manifestations  concomitant  with  activity  in  the 
muscle,  e.g.  the  resulting  changes  in  optical  properties,  have  been 
described  in  the  previous  section.  The  chemical  constitution  of 
muscle -substance,  and  its  alterations  in  activity,  can  best  be 
studied  in  recent  text-books  of  Physiological  Chemistry.  There 
remains  for  consideration  the  most  striking  manifestation  of 
muscular  activity,  i.e.  change  of  form  {contraction).  The  most 
essential  feature — contraction  in  a  longitudinal  direction  icith  simul- 
taneous expansion  (increase  of  cross-section) — appears,  as  a  matter 
of  course,  in  all  cases  where  the  contractile  particles  of  proto- 
plasm lie  permanently  or  temporarily  in  a  definite  direction. 
This  has  already  been  pointed  out  re  the  more  or  less  rapid, 
sometimes  instantaneous,  shortening  and  thickening  of  certain 
forms  of  pseudopodia  {Myopodien,  Myopliryskcri),  as  well  as  in  the 
myoid  layer,  or  myonema,  of  certain  infusoria,  which  must  be 
regarded  as  true  muscle.  Indeed,  the  same  changes  of  form  may 
be  observed,  as  it  were,  in  an  elementary  stage  in  single  fibrils, 
or  bundles  of  fibrils,  that  reappear  in  the  highly-complex,  multi- 
cellular organs  which  it  is  usual  to  designate  as  muscles  in  more 
highly-organised  animals.  In  every  case  the  mechanical  effect  of 
change  of  form  in  a  muscle  depends  upon  its  shortening  in  a 
longitudinal  direction — never  upon  its  thickening.  Hence  it  is 
customary  only  to  speak  of  shortening,  or  contraction,  with  refer- 
ence to  muscle-activity. 

We  have  already  stated  in  discussing  the  manifestations  of 
activity  in  the  myoideum  that  a  single  stimulus  of  very  short 
duration,  e.g.  a  single,  quick  alteration  of  density  in  an  electrical 
current,  or  the  shortest  possible  mechanical  impact,  produces  an 


CHAP.  II      CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  55 

equally  rapid  contraction,  with  much  slower  subsequent  elongation. 
A  rapid  contraction  of  this  kind,  which  is  especially  characteristic 
of  striated  muscle,  is  termed  a  "  tivitcli!'  This  elementary  form 
of  activity  is,  however,  by  no  means  peculiar  to  muscle,  since,  on 
the  one  hand,  the  rhythmical,  or  even  non-rhythmical,  movements 
of  a  ciliated  element  may  be  regarded  as  consisting  of  single,  con- 
secutive twitches,  many  flagella  also  "  twitching  "  in  contraction  ; 
and,  on  the  other,  many  muscles — the  uninuclear,  smooth  muscle- 
cells  in  particular — contract  so  slowly  that  it  is  as  impossible  to 
speak  of  "  twitch  "  in  these  as  in  the  far  more  sluggish  contraction 
of  the  pseudopods  in  most  Ehizopoda. 

A  "  twitching "  contraction  seems  invariably  to  denote  the 
presence  of  fibrillated  structure  (more  especially  with  cross- 
striation),  although,  as  we  see  in  smooth  muscle-cells,  the  differ- 
entiation of  fibrils  does  not  on  the  other  hand  invariably  produce 
a  very  rapid  contraction. 

In  the  most  characteristic  case  of  the  "  twitch,"  contraction, 
as  far  as  can  be  seen,  begins  simultaneously  with  the  cause  of 
excitation,  reaches  its  maximum  as  quickly  as  possible,  and  then 
dies  out  again  in  sloiu  relaxation.  The  very  marked  difference 
which  appears  between  the  duration  of  contraction  on  the  one 
hand,  and  elongation  on  the  other,  in  the  contractile,  twitching 
parts  of  the  lowest  animal-forms  (stem  of  vorticella,  spirostomum, 
myopodia,  etc.),  is  due  in  great  part  to  the  peculiar  mechanical 
relations  which  here  govern  contraction  and  relaxation.  The 
twitching  fibrils  behave  more  or  less  like  an  unloaded  muscle, 
swimming  in  mercury,  which  only  recovers  its  normal  length 
when  an  extending  force  is  acting  upon  it.  The  course  of  a 
single  twitch  is  usually  so  rapid  that  it  is  impossible,  from  direct 
observation,  to  detect  any  minutise  in  regard  to  the  time-relations 
of  the  contraction,  and  behaviour  of  the  contractile  fibres,  in 
the  individual  stages  of  shortening.  Finer  artificial  means  of 
measuring  tune  are  necessary  in  order  to  ascertain  the  relations 
of  the  different  phases  within  the  brief  act  of  a  single  contrac- 
tion.^ 

As  a  means  of  measuring  such  minute  intervals  as  are  here 
under  consideration,  preference  must  undoubtedly  be  given  to  the 

1  Cf.  V.  Bezold,  Untersucliungen  ilher  die  elektrische  Erregung  der  Nerven  u.  Mus- 
keln,  1861,  p.  31.  (Historical  survey  of  attempts  to  measure  the  minute  time- 
intervals  occupied  by  nerve  and  muscle  action.) 


56 


ELECTRO-PHYSIOLOGY 


graphic  tracing  of  the  process  to  be  measured,  upon  a  rapidly- 
moving  surface.  If  such  a  surface  (of  smoked  glass  or  paper) 
moves  with  sufficient  velocity  past  the  point  of  a  recording  lever 
attached  to,  and  following  the  contraction  of,  the  twitching 
muscle  to  which  it  is  attached,  a  curve  is  obtained,  the  abscissa 
of  which  corresponds  with  the  time,  the  ordinates  on  the  other 
hand  with  the  magnitude  of  the  contraction  (expansion)  of  the 
muscle.  This  is  the  principle  of  the  Helmlwltz  Myogra-ph,  which  has 
been  followed  by  a  number  of  similar  instruments,  as  described 
in  every  text-book. 

The  time  value  of  the  abscissa  in  every  such  "  contraction 
curve  "  is  easily  determined  if  the  speed  of  the  travelling-surface 
is  known,  or  if  a  tuning-fork  tracing  is  taken  simultaneously  with 
the  "myogram." 

The  application  of  the  graphic  method  enables  us  at  once,  and 
simultaneously,  to  recognise  the  peculiarities  characteristic  of  the 


Fig.  33. — Curve  of  muscular  contraction.    (Helmholtz.)    a,  Moment  of  excitation. 

process  to  be  examined,  in  magnitude,  form,  and  duration.  If  the 
moment  of  stimulation  is  marked  upon  the  recording  surface,  the 
rise  of  the  lever"  from  the  abscissa  does  not  usually  coincide  with 
the  moment  of  stimulation,  but  occurs  distinctly  later,  i.e.  the 
muscle  does  not  begin  to  shorten  at  the  moment  at  which  the 
induction  shock  takes  effect,  but  a  given  time  elapses  before  the 
charges  produced  by  excitation  bring  about  contraction,  as  ex- 
pressed in  the  movement  of  the  lever  (Fig.  33). 

The  length  of  this  time,  measured  between  a  and  the  begin- 
ning of  the  curve  along  the  abscissa,  was  estimated  by  Helmholtz 
at  about  0*0 1  sec.  for  a  loaded  frog's  muscle  directly  excited  by  an 
induction  shock.  It  is  known  as  the  period  of  latent  stimulation 
(latency  period),  because  during  this  time  no  visible  mechanical 
effect  is  produced  by  the  stimulus.  Contraction  of  the  muscle 
begins  when  the  discharging  stimulus  has  ceased,  and  is  marked 
by  the  rising  of  the  lever  to  the  summit  of  the  curve.      From 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  57 

this  point  the  muscle  lengthens  slowly  until  it  reaches  its 
original  dimensions.  The  interval  between  the  beginning  of  the 
contraction  and  its  maximum  is  known  as  the  period  of  rising 
energy,  that  from  the  maximum  to  complete  extension  of  the 
muscle  as  the  period  of  falling  energy  ;  the  entire  period  from  the 
beginning  of  the  contraction  to  complete  extension  represents  the 
duration  of  the  contraction. 

In  regard  to  the  amplitude,  or  height,  of  muscular  contraction, 
it  must  be  remembered  that  there  is  generally  a  more  or  less 
considerable  enlargement  in  graphic  records,  and  that  the  length 
of  the  recording  lever  must  always  be  taken  into  consideration,  if 
the  real  magnitude  of  contraction  is  to  be  determined.  The  two 
stages  of  rising  and  falling  energy  may  easily  be  determined  if  an 
ordinate  is  drawn  from  the  top  of  the  curve,  vertical  to  the  abscissa. 
As  a  rule  the  first  is  distinctly  shorter  than  the  second,  but  the 
opposite  may  occur  {e.g.  on  cooling).  With  regard  to  the  form  of 
the  contraction  curve  it  must  be  remarked  that  in  many  instances 
we  cannot  regard  it  as  a  complete  expression  of  the  process  of 
movement,  since  the  recording  lever  is  frequently  arranged  (apart 
from  possible  spontaneous  variations)  so  that  its  point  describes 
the  arc  of  a  circle  in  moving.  The  velocity  of  the  travelling 
surface  has  also  a  considerable  effect  upon  the  form  of  the  curve 
— one  and  the  same  movement,  recorded  by  the  same  lever, 
yields  very  different  curves,  according  as  the  myograph  plate 
travels  fast  or  slowly. 


I. — Dependence  of  the  Peogess  of  Contraction  upon  the 
Nature  of  the  Muscle 

The  marked  differences  which  exist  in  regard  to  the  rate  of 
movement  as  manifested  in  different  kinds  of  protoplasm,  lead 
us  a  priori  to  anticipate  that  similar  distinctions  must  exist  in 
the  muscles  of  different  animals  as  well  as  in  the  different  muscles 
of  the  same  species,  as  might  be  inferred  at  once  from  their  fun- 
damental differences  of  structure.  And  indeed  the  merest  glance 
shows  that  without  considering  other  external  influences  yet  to  be 
mentioned,  the  form  and  process  of  contraction  are  essentially 
dependent  on  the  nature  of  the  muscle.  Above  all,  we  are  im- 
pressed  by  the  enormous   difference    exhibited   between    smooth 


58  ELECTRO-PHYSIOLOGY 


47iuscle  and  striated  muscle.  The  contractions  of  smooth  muscle 
are  incomparably  slower  than  those  of  striated  muscle,  so  that  we 
could  never  speak  of  a  "  twitch "  when  a  single  stimulus  was 
acting  on  the  elements  of  smooth  muscle.  The  entire  course  of 
contraction  is,  so  to  speak,  macroscopic,  since  the  latent  period,  as 
well  as  all  the  phases  of  contraction  and  elongation,  can  be  con- 
veniently followed  by  the  eye  without  artificial  assistance. 

Midway  between  these  sluggishly  contracting  smooth  muscles 
and  the  "twitching,"  striated  muscles  of  invertebrates  and  verte- 
brates stand  the  uninuclear,  cross-striated  elements  of  cardiac 
muscle,  where  contraction  is  neither  so  sluggish  as  in  smooth,  nor 
so  rapid  as  in  most  striated  skeletal  muscles.  For  this  reason 
it  was  long  a  matter  of  dispute  whether  the  single  contraction 
of  the  heart,  discharged  by  a  momentary  excitation  (which 
in  no  way  differs  from  a  natural  "  heart-beat "),  is  really  com- 
parable with  the  elementary  single  twitch  of  a  skeletal  muscle. 
But  that  it  is  so  cannot  now  be  doubted.  It  is  clear  that  its 
longer  duration  is  no  sort  of  proof  that  the  single  contraction  of 
cardiac  muscle  does  not  correspond  with  a  simple  twitch.  Even 
among  the  striated  skeletal  muscles  of  different  animals,  or  the 
muscles  of  the  same  individual,  considerable  differences  may 
occur,  as  we  have  seen,  in  regard  to  rapidity  of  contraction,  and 
it  is  easy  to  produce  these  artificially  to  a  much  greater  extent 
than  is  the  case  in  normal  cardiac  contraction. 

We  shall  therefore  assume  that  every  single  contraction  of 
cardiac  muscle  {vertebrate  or  invertehrate),  whether  natural  or  pro- 
duced hy  a  hrief  artificial  stimulus,  is  an  elementary  "  twitch," 
although  retarded  and  protracted  in  all  its  phases. 

If,  under  approximately  equal  conditions,  the  contractions  in 
the  heart  and  skeletal  muscle  of  the  frog,  excited  by  a  single 
induction  shock,  are  recorded  by  the  graphic  method  with  a 
lightly  attached  lever,  it  will  be  found,  as  Marey  pointed  out  (1), 
that  the  heart-curve  and  muscle-curve  exhibit  in  respect  of  form 
the  same  characteristic  peculiarities  of  rapid  rise,  and  more 
gradual  sinking. 

The  latent  period  is, however, without  exception,  longer  in  cardiac 
than  in  skeletal  muscle  under  the  same  conditions,  and  the  more 
conspicuously  so  in  proportion  with  the  difference  in  rapidity  of 
contraction  between  the  two  kinds  of  striated  muscle.  As  this 
difference  is  greater  in  poikilo-thermic  vertebrates  than  in  the 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  59 

warm-blooded  animals,  the  difference  in  the  length  of  the  latent 
period  is  more  marked  also.  Thus  in  the  frog  the  latent  period 
of  cardiac  muscle  may  last  0'28  sec,  while  in  the  gastroc- 
nemius of  the  same  animal  it  is  only  O'Ol  sec.  according  to 
Helmholtz,  and  still  shorter  (0"005  sec.)  according  to  the  latest 
observations.  The  period  of  rising  energy  is,  in  the  frog's  heart, 
2—3  sees,  according  to  Marchand  (2),  while  the  same  period 
in  skeletal  muscle  must  be  measured  by  fractions  of  a  second. 
The  striated  muscles  of  the  medusae,  which  approximate  to  cardiac 
muscle  in  other  respects  also,  are  characterised  by  a  similar 
sluggish  contraction  (Eomanes,  3), 

Similar,  if  less  extensive,  differences  in  the  time-relations  of 
contraction  have  recently  been  shown  to  exist  within  striated 
skeletal  muscle  itself,  and  that  not  merely  in  different  animals, 
but  in  one  and  the  same  individual,  even  within  one  muscle. 
It  may  he,  said,  speaking  generally,  that  there  are,  in  a  2Jhysiological 
sense,  tivo  kinds  of  imdtinuclear,  cross-striated  muscle-fibres,  charac- 
terised respectively  by  ra'pid  and  hy  sluggish  contraction  ("  quick  "  and 
"  sluggish  "  muscles).  Between  the  two  there  are  innumerable 
intermediate  stages. 

It  is,  e.g.,  evident  that  the  skeletal  muscles  of  a  tortoise  or 
chameleon,  as  a  rule,  contract  much  more  slowly  than  those  of  the 
frog  or  a  warm-blooded  animal ;  while,  on  the  other  hand,  certain 
muscles  of  insects  contract  more  quickly  than  the  best-adapted 
muscles  of  warm-blooded  animals.  This  is  practically  obvious 
from  the  respective  movements  of  the  creatures,  taking  only,  e.g., 
the  slow  sluggish  movements  of  the  tortoise  in  comparison  with  the 
marvellously  rapid  wing-beats  of  many  insects,  whose  muscle- 
fibres  must  contract  several  hundred  times  in  the  second.  The 
contraction  curve  of  such  muscles  must  be  immeasurably  shorter 
than  that  of  the  frog  or  tortoise.  It  is  probable  that,  as  Hermann 
(4,  p.  38)  suggested,  a  continuous,  graduated  scale  might  be  drawn 
up  in  the  animal  kingdom,  beginning,  after  Marey,  at  the  excess- 
ively rapid  contractions  of  the  wing-muscles  of  insects ;  then 
would  follow  the  striped  skeletal  muscles  of  birds,  fishes,  mammals, 
frogs,  toads,  and  lastly  of  tortoises  and  hibernating  dormice,  then 
cardiac  muscles,  and  finally  most  of  the  smooth  muscle-cells  whose 
contraction  process,  as  we  have  said,  is  macroscopic.  In  frog 
muscles  the  single  twitch  lasts,  at  ordinary  temperature,  from 
0"1  to  0"3  sec,  in  the  tortoise  often  more  than   1   sec,  while  in 


60 


ELECTRO-PHYSIOLOGY 


the  wing-muscles  of  many  insects  the  duration  of  a  contraction 
falls  to  -r^Q  sec,  lasting,  on  the  other  hand,  for  several 
seconds  in  smooth  muscle.  Hand  in  hand  with  these  differences 
in  the  period  of  contraction  are  other  differences  in  the  size  of 
the  mechanical  latent  period,  which,  as  a  rule,  increases  with  in- 
creasing duration  of  contraction. 

The  fact  that  the  striated  muscles  of  the  same  animal  may 
present  very  important  functional  as  well  as  histological  and 
chemical  differences,  is  very  interesting.  Eanvier  (5)  was  the  first 
to  observe  that  the  contraction  period  differed  in  the  pale  and  red 
muscles  of  the  rabbit,  the  red  being  distinguished  from  the  pale 
muscles  by  a  comparatively  long  contraction  period,  and  a  corre- 


FiG.  34. — (t,  Three  maximal  contractions  loaded  at  50,  100,  and  200  grs. ;  h,  four  maximal 
contractions  at  50  to  500  grs.    (Cash.) 


spondingly  longer  mechanical  latent  period ;  the  pale  muscles 
contract  much  more  quickly  after  a  short  latent  period.  In  par- 
ticular, Ranvier  compared  the  function  of  the  red  semitendinosus 
muscle  with  that  of  the  pale  vastus  internus,  or  adductor 
magnus,  in  rabbit,  and  found  on  stimulating  with  single  induc- 
tion shocks  that  it  did  not  contract  quickly  like  the  pale  muscle, 
but  shortened  gradually,  the  latent  period  being  four  times 
greater.  Kronecker  and  Stirling  (6)  confirmed  these  facts,  finding 
the  contractio7i  period  of  red  muscle  nearly  three  times  as  long 
as  that  of  the  j^ale,  tuhile  the  height  of  contraction  of  the  former  ivas 
quite  insignificant  as  compared  ivith  the  pale  muscle  (Fig.  34,  a,  h). 
Marey  had  made  similar  observations  on  the  different  muscles  of 
the  frog,  finding,  e.g.,  that  M.  hyoglossus  was  more  sluggish  than 
gastrocnemius.      Cash  (7)  ascertained  by  conclusive  experiments 


CHAXGE  OF  FORM  IX  MUSCLE  Dl'RIXG  ACTIVITY 


61 


that  ill  both  the  frow  and  tortoise  different  muscles  are  distin- 
giiished  by  characteristic  difterences  in  the  form  and  process  of 
the  curve  of  contraction.  The  average  duration  of  contraction  in 
different  skeletal  muscles  of  the  frog  is  shown  in  the  following 
table  : — 

Sec. 
1.   M.  hyoglossus      ....      0-2-0 -3 

0-17 
0-12 
0-108 
0-104 

Cash  found  the  contraction  period  of  Tcstudo  europa:a  to  be  : — 


2_ 

,,    rectus  abdominis 

3. 

„    gastrocnemius 

4. 

„    semimembranosus 

5. 

,,    triceps 

1.  ^I.  peetoralis  major 


2. 

)5 

glutfeus 

3. 

)? 

palmaris 

4. 

}J 

gracilis 

5. 

!> 

biceps 

6. 

5> 

splenius  capitis 

7. 

55 

triceps  brachii 

8. 

55 

retrahens  colli 

9. 

55 

semimembranosus 

10. 

55 

omohvoideus 

6 
55 


Yet  more  characteristic  than  the  duration  is  the  nature  of  the 
process  (form),  as  expressed  in  the  myograms.  Manj  of  these  have 
such  significant  forms  that  they  ought  in  a  measure  to  indicate  the 
species  of  muscle.  The  accompanying  figure  (Fig.  35a)  shows 
how  differently  gastrocnemius  behaves  from  the  triceps  and  semi- 
membranosus -  gracilis  group.  These  last  muscles  reach  the 
maximum  of  contraction  soon  after  the  half  of  their  entire 
contraction  period,  while  gastrocnemius  takes  two-thirds  of  its 
period  for  contraction,  and  only  one-third  for  extension.  If  the 
following  group  of  the  most  sluggish  frog  muscles  (Fig.  35  b)  is 
compared  with  these  curves,  the  difference  is  very  striking. 

Fig.  35c  of  tortoise  is  even  better  quahfied  to  show  how 
the  contraction  curves  of  different  striated  muscles  may  vary  in 
form  in  the  same  animal.  ]\I.  omohyoideus  contracts  most  rapidly 
in  correspondence  with  its  function  of  withdrawing  the  head  of 
the  animal  quickly  under  the  protecting  carapace  when  m  danger, 
while  the  }:iowerfiil  peetoralis  major,  which  serves  the  movements 
of  the  heavy  animal,  "  begins  with  an  energetic  lift,  and  delays 
some  time  at  the  apex  of  contraction."      Similar  difterences  should 


62 


ELECTEO-PHYSIOLOGY 


exist  between  the  rapidly  moving  eye-  and  tongue-muscles  and 
the  sluggish  skeletal  muscles  of  the  chameleon. 

It  must  further  be  remarked  that  both  the  relative  and 
absolute  height  of  twitch  is  much  greater  in  the  quick  muscles  in 
the   frog   than    in    the   sluggish  muscles. 


A  rectus  abdominis 


Fig.  35a. — Contraction  curve  of  three  different  muscles  of  Frog  under  uniform  conditions. 

(Cash.) 


Fig.  35b. — Four  contraction  curves  of  different  muscles  of  Frog.     (Cash.) 


Omo  hpoW/ 


Sector  maj. 
Jjrarilis 


Fig.  35c. — Four  contraction  curves  of  different  muscles  of  Tortoise  under  uniform  conditions.     . 
The  time-tracing  is  in  secomls. 

muscle  of  B.  csculenta,  32  mm.  long,  contracted  about  2-6  times 
less  frequently  at  medium  tension  than  the  gastrocnemius,  which 
was  only  28  mm.  long.  The  height  of  lift  recorded  (enlarged) 
amounted  to  6  and  15  mm.  The  sluggish  hyoglossus,  26  mm., 
has,  at  approximately  proportional  tension,  a  height  of  twitch  of 
1"5  mm.  only  (Grlitzner). 

EoUett  (8)  has  recently  pointed  out  a  remarkable  instance  of 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  63 

sluggish  contraction  in  warm-blooded  muscles.  We  have  already 
alluded  to  the  peculiarities,  especially  the  abundance  of  sarco- 
plasm,  by  which  the  striated  muscles  of  the  bat  are  distinguished. 
Experimental  excitation,  with  single  induction  shocks,  shows  that 
the  process  of  contraction  in  these  conspicuously  "  dark  "  muscles 
(pectoralis  major,  biceps,  and  triceps)  is  remarkably  sluggish. 
EoUett  reckons  an  average  of  0-025  sec.  for  the  latent  period, 
0'146  sec.  for  the  ascending  period  of  the  curve,  0"350  sec.  for 
the  descending  period,  i.e.  0'496  sec.  for  the  total  contraction. 
Hence  these  muscles  appear  more  sluggish  than  any  in  the  frog, 
but  quicker  than  those  of  the  tortoise,  quicker  than  the  red 
muscles  of  rabbit,  but  much  slower  than  pale  muscle  in  the  same 
animal.  The  differences  in  the  contraction  process  of  anatomically 
separate  muscles  in  the  same  animal  are  very  striking  also  in 
many  invertebrates.  Ch.  Eichet  (9)  found  very  different  curves 
of  contraction  in  the  tail  and  claw  muscles  of  the  crayfish,  whether 
the  contraction  was  discharged  centrally  or  by  artificial  excita- 
tion. The  curve  of  the  tail-muscles  is  short,  and  similar  to  the 
gastrocnemius  contraction  of  the  frog.  The  adductor  of  the  claw, 
on  the  other  hand,  described  an  extended  curve,  which  differs 
essentially  from  that  of  the  tail-muscles.  This  statement  once 
more  tallies  with  the  normal  movements  of  the  parts  in  question 
(rapid  flapping  of  the  tail,  sluggish  but  protracted  closing  of  the 
claws).  The  greatest  disparity  in  this  direction  might  be  ex- 
pected between  the  wing  and  other  body-muscles  of  insects,  for 
the  wide  histological  differences  between  them  are  an  a  priori 
indication  of  corresponding  functional  modifications.  Unfortu- 
nately there  are  no  adequate  observations  as  to  the  contraction 
process  in  the  former ;  it  is  only  known  that  they  do  contract 
with  extraordinary  rapidity.  Eollett  has  recently  communicated 
some  interesting  experiments  on  the  physiological  divergences 
in  muscles  bearing  the  same  name,  but  histologically  different,  in 
insects  (beetles)  which  are  otherwise  very  similar  (10).  The 
skeletal  muscle-fibres,  collectively,  of  Dy tiscus  differ  fundamentally 
in  structure  from  those  of  Hydrophilus,  while  each  beetle  possesses 
a  perfectly  uniform  structure  of  its  own  muscle-fibres.  Dytiscus 
exhibits  in  a  cross-section  ilio,  fiat  muscle-columns,  and  correspond- 
ing radial  arrangement,  of  Cohnheim's  Are?e,  from  which  the 
rays  of  sarcoplasm  stream  out  featherwise  from  the  large  accumu- 
lation round  the  nuclei  (Fig.  25).     Hydrophilus,  on  the  contrary, 


64 


ELECTRO-PHYSIOLOGY 


exhiljits  ijolygonal  Cohnheim's  Arese,  with  a  central  cavity  filled 
with  sarcoplasm ;  each  muscle-column  is  penetrated  by  a  central 
canal,  and  uniformly  bordered  by  sarcoplasm.  EoUett  employed 
preparations  of  these  beetles,  in  which  the  muscles  that  work  the 
thigh  of  the  hind  pair  of  legs  were  directly  excited  by  induction 
shocks.  These  experiments  exhibited  a  fundamental  difference 
in  form  and  duration  of  the  single  contraction  in  the  two  species. 
The  curve  of  Dytiscus  rises  abruptly  to  the  maximum  of  contrac- 
tion, and  then  sinks  quickly  back  to  the  abscissa.  The  curve  of 
Hydrophilus  reaches  its  maximum  much  later,  maintains  it  for  a 
longer  time,  and  then  sinks  gradually  (the  myogram  of  cockchafer 
muscle  is  even  more  extended)  (Fig.  36).      The  course  of  contrac- 


FiG.  36. — A,  Contraction  curve  of  leg-muscle  of  Dytiscus;  B,  of  Hydrophilus ;  C,  of  Melolontlia; 
traced  at  uniform  rate  of  tlie  recording  surface.    (Rollett.) 


tion  in  Dytiscus  is  therefore  comparable  with  that  of  the  pale 
muscle,  of  Hydrophilus  and  Melolontha  with  that  of  the  red 
muscle,  in  rabbit.  For  the  rest,  the  absolute  duration  of  a 
twitch  and  its  component  periods  varies  in  every  case  within 
tolerably  wide  limits.  The  following  table  from  Piollett  gives  the 
averages  of  a  great  number  of  single  experiments  : — 


Beetle. 

Latent  Period. 

Duration  of 
Contraction. 

Ascending  Por- 
tion of  Curve. 

Descending 
Portion  of  Curve. 

Dytiscus    . 
Hydrophihts     . 
Melolontha 

Sec. 
0-017 
0-047 
0-075 

Sec. 
0-112 
0-350 
0-527 

Sec. 
0-055 
0-108 
0-110 

Sec. 
0-057 
0-242 
0-411 

If  this  is  compared  with  the  numbers  given  by  Marey  (11) 
as  the  possible  rate  of  contraction  per  second  in  the  wing-muscles 
of  different  insects,  the  extraordinary  disparity  of  the  two  kinds 
of  muscle  is  most  clearly  established  : — 


CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY 


House-fly     . 

330 

Humble-bee 

240 

Bee 

190 

Wasp 

110 

Dragon-fly   . 

28 

Cabbage  Butterfly     . 

9 

Again  we  see  that  the  respective  properties  of  the  muscles  are 
more  or  less  clearly  expressed  in  the  movements  of  the  uninjured 
animal. 

Thus  it  is  proved  that  not  only  the  striated  muscles  of 
different  animals,  but  those  of  the  same  species  also,  exhibit 
fundamental  differences  in  regard  to  the  time -relations  of  the 
process  of  contraction.  Griitzner's  investigations  show  that  the 
same  holds  good  for  the  fibres  of  the  single  muscle  also.  Just  as 
there  are  quick  muscles  and  sluggish  muscles,  so  in  many,  and 
perhaps  most,  cases  there  are  quick  and  sluggish  muscle- fibres 
in  one  anatomical  muscle.  As  early  as  1805,  Patter  pointed 
out  a  physiological  difference  in  different  groups  of  muscles, 
crediting  the  flexors  of  the  frog  with  a  lower,  "  conditioned,  and 
finite,"  the  extensors  with  a  more  considerable,  "  unconditioned, 
infinite  "  excitability.  We  shall  have  to  consider  these  facts  else- 
where in  detail ;  here  it  is  enough  to  say  that  later  experiments 
(particularly  of  EoUett)  show  that  in  electrical  excitation  of 
the  sciatic  nerve  the  flexors  are  mainly  excited  by  weak,  the 
extensors  by  stronger,  currents.  Griitzner  (12)  subsequently  ascer- 
tained that  the  flexor  muscles  of  the  frog,  with  direct  excitation, 
as  well  as  indirectly  from  the  nerve,  contract  much  earlier,  and 
much  more  rapidly,  than  the  extensors,  as  is  most  obvious 
with  normal  circulation  and  non  -  fatigue  of  both  kinds  of 
muscle. 

In  the  first  instance,  this  is  only  a  further  illustration  of  the  same 
proposition — that  different  muscles  of  the  same  animal  may,  under 
certain  conditions,  exhibit  a  different  contraction  period,  and,  it 
may  be  added,  different  excitability.  We  shall  have  occasion  to 
refer  to  yet  another  observation  of  Eanvier,  according  to  which 
the  triceps  humeri  of  rabbit — consisting  both  of  red  (sluggish) 
and  pale  (quick)  fibres — contracts  quickly  at  the  beginning  of  a 
long  excitation  series  like  an  unmixed,  "  pale "  muscle,  owing  to 
the  greater  excitability  of  the  pale  fibres,  but  later  on,  when 
fatigued,  sluggishly,  like  red  muscle,  because  the  more  excitable 

F 


66  ELECTRO-PHYSIOLOGY 


quick  fibres  are  more  easily  exhausted  than  the  sluggish,  but 
enduring,  red  fibres. 

Grlitzner  finds  the  same  reaction  in  the  flexors  and  extensors 
of  the  frog's  foot.  If  in  bloodless  legs,  the  sluggish  extensors 
and  quick,  excitable  flexors  are  made  to  serve  up  frequent 
contractions,  the  initial  difference  in  contraction  process  will 
completely  disappear,  or  even  reverse  itself.  That  is  to  say,  the 
flexors — composed  mainly  of  easily  excitable,  quick  fibres — are 
more  easily  fatigued  than  the  characteristically  sluggish,  resistant 
extensors.  This  is  demonstrated  by  the  following  experiment 
(Grlitzner,  Z.c.)  If  the  iliac  artery  of  the  frog  is  tied  on  one  side, 
the  animal  at  first  springs  as  if  normal  in  the  direction  of  its 
long  axis,  since  the  extensors  (gastrocnemius)  of  both  sides  are 
able  to  function  equally ;  soon,  however,  the  animal  leaves  the 
leg  of  the  tied  side  extended,  and  only  draws  it  up  later — after 
its  spring — to  the  body:  the  excitability  of  the  flexors  has 
already  been  diminished  by  the  short  anaemia. 

Where  a  single  muscle  is  composed  of  two  groups  of  fibres, 
differing  physiologically  as  above,  and  provided  the  one  group 
does  not  preponderate  too  much  over  the  other,  the  contraction 
curve  (with  sufficiently  strong  excitation)  must  obviously  be 
regarded  as  a  combination  of  two  curves,  differing  in  form  and 
time -relations,  as  can  even  occasionally  be  detected  in  the 
myogram.  We  have  actually  been  familiar  for  a  long  time  with 
certain  peculiar  double-topped  curves  of  contraction,  and  their 
origin  now  becomes  intelligible  (13).  In  many  cases,  provided 
the  "  sluggish "  fibres  do  not  lag  too  far  behind  the  "  quick " 
fibres,  they  also  come  into  play  at  the  first  excitation ;  the  curve 
is  double-topped  from  the  beginning,  as,  e.g.,  in  the  gastrocnemius 
group  of  the  rat  (14),  and  usually  the  frog's_  sartorius.  In 
other,  and  indeed  most,  cases,  where  the  quick  fibres  are  in  the 
ascendant,  the  mixed  fresh  muscle  commonly  contracts  at  the 
first  effort  of  artificial  excitation  as  if  composed  of  quick  fibres 
only — the  simultaneously  excited,  but  slower,  and  more  sluggish 
portion  being  merely  drawn  along  with  the  other.  But  if  the 
quick  part  be  more  and  more  fatigued,  the  sluggish  fibres  come 
into  action,  and  the  curve  becomes  double-topped  (15). 

The  difference  in  excitability  and  contraction  between 
the  quick  and  sluggish  fibres  is  well  exhibited  in  chemical 
excitation  of  the  sartorius  (Grlitzner,  16).      If  the  upper  surface 


11  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  67 

of   this    muscle- — just    beneath    the    skin — is    moistened    with 
a   1-2   ° I ^   sokition    of  potassium  nitrate,  the   muscle    shrinks 
slowly    together ;    if    the    under    surface    is    stimulated    in    the 
same  manner  there  is  little  or  no  result.      The   whole  muscle, 
however,  contracts  instantaneously  if  electrically  excited   by   an 
induction  shock.     The  cause  of  this  striking  reaction  is,  according 
to  Griitzner,  that  the  sartorius  of  the  frog  consists  of  two  layers 
of  different  muscle-fibres,  of  luhicli  the  wpper  {sluggish)  layer  con- 
tracts more  slowly  than  the  under  {quick)  layer,  and  while  only  the 
first  is  excited  hy  the  potassium  salt,  both,  hut  especially  the  quick, 
react    to    the    electrical    stimulus.      So,    too,   many   warm-blooded 
muscles   (particularly  if  thin,  e.g.  muscles  of   belly,  diaphragm), 
when  curarised.      If  dabbed  with  salt  solution  they  draw  slowly 
together  (peristaltic  action) ;  but  if  the  same  place  is  electrically 
excited  before,  or  after,  with  an  induction  shock,  contraction  is 
con\ailsive  and  instantaneous.      All  this   evidence  goes  to  show 
that  a  muscle,  in  many  cases,  has  no  physiological  unity,  but  is  a 
mixture  of  at  least  two  functionally  different  elements,  which,  in 
the  normal  movements  of  the  animal,  serve  for  distinct  purposes, 
as  appears  from  the  correspondence  of  the  mode  of  movement  of 
an  organ,  or  single  muscle,  with  the  number  of  quick  or  sluggish 
fibres  which  characterise  its  movement.      It  is  also  instru.ctive 
that  (as  Eollett  pointed  out)  there  are,  besides  the  thoracic  fibrils 
— characterised   by   their   extremely  rapid   contraction — in    the 
wings  of  certain  insects,  other  muscles,  which  are  quite  distinct 
anatomically  and  physiologically,  and  are  of  very  inconsiderable 
bulk  as  compared  with  the  others  (the  wing-muscles  proper).     The 
presence  of  two  kinds  of  muscles  is  in  obvious  relation  with  two 
distinct   actions.      One    of  these   is  the  unfolding  of  the  wing- 
apparatus,  arrangement  of  the  wing-cases,  and  spreading  of  the 
wings.      This  action  resembles  the  leg-movements.      The  second 
action,  on  the  contrary,  is  that  of  actual  flight,  which  has  been 
shown  by  Marey  to  depend  upon  an  extraordinary  frequency  of 
the  beat  of  the  wings  in  insects.      In  this  case  the  anatomical 
difference  between  quick  and  sluggish  fibres  is  very  significant, 
and    the  thoracic  fibrils  are  accordingly  distinct  on  anatomical 
as  well  as  physiological   grounds.      They  comprise  to   a  certain 
extent  all  those  properties  which  are,  as  a  rule,  characteristic '  of 
muscles  that  contract  permanently  and  quickly,  i.e.  great  abund- 
ance of  sarcoplasm,  and  a  marked  development  of  cross-striation. 


ELECTRO-PHYSIOLOGY 


The    histological    differences    between    quick    and     sluggish 
muscles  are  much  less  in  the  majority  of  cases.      As  a  rule  it 
may  be  said  that  the  latter,  at  least  in  vertebrates,  are  richer  in 
sarcoplasm,   dark,    and   often   smaller ;  while    the   quick,   excitable, 
more  easily  fatigued  muscle-fibres  contain  less  sarco'plasm,  and  are 
therefore  clearer  and  usually  broader.     As  shown  above,  the  dark 
fibres  are  often,  though  not  invariably,  stained  by  hsemogiobin 
and  other  colouring  matters.      This  is  very  conspicuous  in  the 
Pecten  family,  where  the  greater  (yellowish-gray)  portion  of  the 
adductor  muscle  consists  of  striated,  the  (whitish)  remainder  of 
smooth,  muscle -cells.      As    Coutance   and   Thoring   showed,    the 
former   serves   only    the   raiAd   closing   of  the   shell,  while   the 
smooth  muscle  closes  it  slowly,   but  permanently  and  forcibly. 
This  becomes  impossible,  and  the  shell  gapes  open,  if  the  smooth 
part   of  the   muscle  is   cut  through ;  the  striated  part  can  still 
effect  rapid   closure   on   excitation,  but   never  of  long  duration. 
The  nicety  of  such  an  arrangement  is  obvious.      Coutance  (18), 
and   later   Knoll   (17),    showed    the    marked    difference    in    the 
contraction  process  between  the  smooth  and  striated  parts  of  the 
adductor  muscle  when  directly  excited.      Lima  inflata  (according 
to  Knoll)   behaves   like  Pecten ;  its   adductor  muscle  does  not, 
indeed,  consist   of  two    macroscopically  distinct   portions,  but  it 
contains  smooth  elements  in  many  layers  at  the   periphery,  and 
singly  in  the  interior,  while  the  bulk  of  the  muscle  is  composed 
of  cross-  (or  obliquely-)  striated  cells.      When  undisturbed  in  sea- 
water,  the  shells  of  these  muscles  usually  gape  open  pretty  widely, 
but  from  time  to  time  they  are  sharply  closed,  and  this  move- 
ment, as  in  Pecten,  jerks   the  animal  a   step  farther.      In   the 
Oyster  also  the  adductor  muscle  consists  of  two  parts,  one  trans- 
parently gray,  the  other  white  and  tendon-like  ;  in  Mytilus  only 
the  white,  in   Solen   only  the  gray  are  present.      Schwalbe,  who 
was    first    to    recognise    that    the   gray   part   consisted    of    "bi- 
obliquely   striated  "  muscle-cells,  also  pointed  out  the  functional 
differences  between  the  two  portions.      If  the  act  of  adduction  is 
compared  in  the  shell  of  Ostrea  and  Mytilus  the  first  is  seeii  to 
close  sharply  and  suddenly  with  external  excitation,  the  second 
very  slowly  and  gradually,  so  that  the  adductor  muscle  can  be 
divided   while   the   shell  is   open,  and  the  knife  is  not  wedged 
in,  as  would  happen  in  the  oyster.      Schwalbe  therefore  thinks 
that  the  bi-obliquely  striated  fibres  of   Ostrea  serve  for   sharp, 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  69 

energetic  contractions,  while  the  longitudinal  fibrils  in  this 
case  also  produce  permanent  closure.  In  Anodonta,  where  a 
similar  differentiation  of  the  adductor  muscle  is  shown  in  two 
sections  visible  to  the  naked  eye,  neither  Engelmann  nor  Bieder- 
niann  was  able  to  detect  any  perceptible  difference  in  rate 
of  contraction  between  the  differently  coloured  parts  of  the 
muscle  (19). 

II. — Dependence  of  Musculah  Contraction  upon  Strength 

OF  Excitation 

A  systematic  inquiry  into  this  point  is  best  effected  with  the 
aid  of  electrical  excitation,  in  the  form  of  single  induction  shocks, 
the  strength  of  which  can  be  graduated  in  the  finest  proportions. 
We  are  thus  in  a  position  to  determine  the  law  of  dependence  of 
contraction  upon  strength  of  excitation.  It  is  easily  proved  that 
below  a  certain  minimal  limit  of  intensity  {the  threshold  of 
stimulation)  the  excitation  produces  no  visible  effect ;  the  dis- 
charge of  a  contraction  begins  first  with  a  given  strength  of 
excitation,  and  its  magnitude  (height)  increases  for  some  time, 
according  to  Fick,  in  proportion  with  increased  strength  of 
stimulus.  Beyond  a  certain  point,  however,  the  increase  in  con- 
traction ceases,  and  the  existing  maximum  is  maintained  for  each 
increment  of  stimulation.  This  maximal  limit  is  usually  but 
little  above  that  at  which  the  first  just  perceptible  contraction 
was  yielded.  The  entire  process  of  this  greatest  contraction  and 
extension  is  known  as  a  maximal  contraction.  It  may  be 
described  in  Tick's  words  (20)  by  saying,  "Each  impact  of 
excitation  discharges  either  a  maximal  contraction  or  no  contrac- 
tion at  all ;  it  is  only  in  a  limited  interval  of  the  scale  of 
excitation  (often  hard  to  find  on  account  of  its  narrow  propor- 
tions) that  sub-maximal,  so  to  say,  imperfect,  contractions  are 
given."  We  shall  presently  see  that  there  are  muscles  (heart) 
which  yield  only  maximal  contractions. 

The  law  of  approximately  proportional  increase  in  height  of 
contraction  within  the  given  narrow  interval,  deduced  by  Pick 
from  experiments  on  indirect  excitation  of  skeletal  muscle,  was 
subsequently  disputed  by  Tigerstedt  (21),  who  found  (with  direct 
excitation  of  curarised  muscle  also)  "  that  with  uniform  increase  of 
strength   in    the   electrical   stimulus,   the   muscular    contractions 


70  ELECTRO-PHYSIOLOGY 


increase  quickly  at  first,  and  then  more  and  more  slowly  (prob- 
ably in  the  form  of  a  hyperbola),  nntil  they  finally  reach  an 
asymptotic  maximum"  (I.e.  p.  16),  a  proposition  which  Hermann 
had  also  put  forward  (4,  p.  108).  Cardiac  muscle  seems,  as  was 
said  above,  at  first  sight  to  differ  from  all  the  striated,  skeletal 
muscles  in  its  lack  of  correspondence  between  strength  of  excita- 
tion and  magnitude  of  resulting  contraction.  It  appears  from 
Bowditch  and  Kronecker  (22)  that,  under  all  conditions,  induction 
currents  of  a  given  intensity  produce  maximal  twitches  of  the 
previously  resting  muscles  of  the  ventricle  ;  weak  stimuli  produce 
no  effect,  while  stronger  stimuli  elicit  no  more  than  the  minimal 
effective  stimulus  ;  minimal  stimuli  arc  therefore,  as  Kronecker  says, 
at  the  same  time  maximal,  and  even  the  most  careful  gradation 
of  the  stimulus  fails  in  the  heart  to  produce  an  incomplete  contrac- 
tion. There  seems  to  be  only  one  exception  to  this  rule,  under  very 
special  circumstances.  Mays  (23),  e.g.,  finds  that  occasionally  in 
the  apex  of  the  frog's  heart,  with  higher  as  well  as  with  lower 
working  capacity,  the  height  of  the  pulse  (twitch)  will  vary  con- 
siderably with  the  strength  of  induction  shocks  sent  in  at  a 
uniform  rhythm.  He  obtains  this  result  most  certainly  when 
the  ventricle  is  filled  with  stale  blood,  and  working  in  the  oil-bath 
of  the  manometer. 

For  the  rest  we  can  but  agree  with  Tick  when  he  sees  in 
these  peculiarities  of  cardiac  muscle  "  the  extreme  development 
of  a  property  common  to  every  other  muscle-fibre,"  since  here 
also  "  the  breadth  of  interval  in  the  scale  of  excitation  for  sub- 
maximal  twitches  stands  in  no  relation  to  the  unlimited  portion 
of  the  same  scale  corresponding  with  the  maximal  contractions." 
This  in  no  degree  solves  the  problem  of  the  latter,  since  it  is 
difficult  to  see  why,  beyond  a  certain  limit,  any  given  strength  of 
stimulus  should  only  produce  quantitatively  equal  responses,  vnhich 
never  correspond  ivith  the  outside  maximum  of  contraction. 

Apart  from  other  facts  to  be  discussed  later,  this  is  evident  ex- 
perimentally, since  what  is  not  produced  by  increment  of  excita- 
tion can  be  obtained  by  rhythmical  repetition  of  uniform  stimuli. 
The  height  of  contraction,  i.e.,  may  increase  under  given  condi- 
tions, when  uniform  induction  currents  are  sent  into  the  muscle 
at  uniform  intervals.  This  striking  effect  was  first  observed  by 
Bowditch,  again  in  cardiac  muscle,  and  confirmed  by  Tiegel  and 
Minot  in  the  skeletal  muscle    of  the  frog,  Eossbach  in  warm- 


CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY 


71 


blooded  muscle,  Eichet  in  the  muscles  of  crab,  and  Eomanes  in 
medusa  (24).  If  uniform  induction  currents  are  sent  rhythmic- 
ally through  the  resting  apex  of  the  frog's  heart,  a  ladder,  or 
"  staircase,"  of  contractions  with  increasing  amplitude  is  almost 
invariably  exhibited,  as  shown  in  the  accompanying  series  of 
curves  (Fig.  37). 

Tiegel  {I.e.  p.  37)  observed  an  analogous  effect  in  curarised 


^I^MA/\y\rt/\ftAAAAm^/WV\M/WV\AAAft^^A/V\^^WV^A^A^^^AA/W^A'\AAAA/\^/WWVWV^^ 


Fig.  37. — Heart  (Frog)  artificially  excited  after  ligature  of  the  sinus.  The  first  notch  of  each  curve 
is  produced  by  the  auricular,  the  proper  summit  by  the  ventricular  systole.  Both  exhibit 
the  staircase.    (Engelmann.) 

frog  muscles  (gastrocnemius)  with  intact  circulation.  If  single 
induction  shocks  of  uniform  strength  are  sent  into  such  a  muscle 
at  regular  intervals,  the  height  of  contraction  increases  constantly, 
so  long  as  maximal  stimuli  are  employed,  even  in  a  series  of 
several  hundred  contractions,  so  that  the  height  of  the  "  stair- 
case "  {i.e.  the  curve  which  unites  the  joint  summits  of  an  ascend- 
ing series  of  contractions)  increases  within  certain  limits  with 


Fig.  38. — Excitation  of  a  somewhat  exhausted  bloodless  gastrocnemius  of  Frog,  by  groups  of 
1,  2,  3,  4,  5,  uniform  maximal  break  induction  shocks.  Increase  in  height  of  contraction 
with  repeated  excitation  at  short  intervals  ("staircase").  Decrease  on  longer  duration  of 
the  pauses  (tuning-fork,  -^^  sec.)    (Engelmann.) 


the  strength  of  the  individual  stimuli.  On  the  application  of 
minimal  stimuli,  there  is,  as  a  rule,  no  increment  of  the  contrac- 
tion series,  or  at  most  a  trace  only,  whereas  in  the  maximal 
series  it  is  invariably  well  developed  (Fig.  38).  If  such  a  series 
is  interrupted  and  resumed  after  a  pause,  the  first  of  the  new 
contractions  is  smaller  than  the  last  before  the  interval  (Tiegel, 
Eossbach,  Buckmaster),  but  the  muscle  immediately  resumes  its 
increasing  contractions.      Within  a  certain  range  it  is  absolutely 


72  ELECTRO-PHYSIOLOGY 


indifferent  at  what  interval  the  periodical  excitations  follow.  A 
maximal  limit  is  only  given  in  order  that  the  stimuli  should  not 
follow  too  slowly,  if  a  "  staircase  "  be  required.  This  maximal 
limit  is  about  60  sees,  for  the  cardiac  muscle  of  the  frog  accord- 
ing to  Bowditch,  about  5  sees,  for  the  striated  skeletal  muscles 
of  warm-blooded  animals  according  to  Eossbach.  The  minimal 
limit  is  determined  by  that  interval  of  stimulation  at  which  the 
series  of  twitches  fuses  into  a  tetanus.  In  regard  to  the  form  of 
the  staircase,  it  should  be  remarked  that  it  is  always,  inde- 
pendent of  strength  and  frequency  of  excitation,  an  equilateral 
hyperbola. 

When  it  is  remembered  that  this  manifestation  is  independent 
of  the  nature  of  the  stimulus  (occurring  equally  with  mechanical 
excitation),  as  well  as  of  the  volume  of  blood  in  the  muscle, 
there  can  be  no  doubt  that  we  are  in  presence  of  a  process  which 
is  intimately  connected  with  the  excitatory  process,  or  contrac- 
tion, in  the  muscle.  We  must  reserve  for  a  later  point  of  the 
discussion  the  probable  cause  of  the  above  reaction,  only  re- 
marking in  conclusion  that  a  similar,  perhaps  more  permanent, 
after-effect  to  that  following  each  single  twitch,  also  appears  after 
a  tetanising  excitation.  Both  Eossbach  {I.e.)  and  Bohr  (25)  found 
that  the  same  excitation  produced  a  greater  effect  (stronger  con- 
traction) after  than  before  the  tetanus.  With  maximal  stimuli 
this  positive  after-effect  often  continues  for  more  than  half .  an 
hour. 

The  latent  period,  as  well  as  the  height  of  muscular  contrac- 
tion, is  partly  dependent  upon  the  strength  of  the  excitation. 
Helmholtz's  estimation  of  the  latent  period  as  0*01  sec.  with 
direct  excitation  of  frog  muscle  (gastrocnemius)  by  single  break 
induction  shocks,  has  been  proved  far  too  large  by  later  investi- 
gators ;  the  variously  estimated  values  of  Place,  Kllinder,  Lauter- 
bach,  Gad,  Mendelssohn  agree  in  showing  that  the  latency  period 
of  frog's  muscle,  directly  excited  with  induction  shocks,  is  only 
from  0-005  to  0-006  sec.  (cf  Tigerstedt,  26).  Tigerstedt  {I.e. 
p.  152)  also  obtained  the  same  result  from  his  own  extensive 
observations.  There  is,  moreover,  the  possibility  that  the  latent 
period  of  muscular  contraction  is  even  less  in  value,  since 
other  significant  data  are  included  in  the  same  computation. 
Burden -Sanderson  (27)  calculates  the  latent  period  of  frog's 
muscle  at   0-0025   sec.   only,  and  Eegeczy  (28)  even  denies   its 


ir  .CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  73 

existence.  Helmholtz  observed  that  in  working  with  induction 
currents  strong  enough  to  produce  the  maximum  of  contraction, 
the  intensity  of  current  may  be  altered  arbitrarily  without  in 
any  way  affecting  the  time -relations.  Tigerstedt  finds  the 
latent  period  of  contraction,  with  direct  maximal  stimulation 
from  break  induction  shocks,  to  be  independent  of  the  strength 
of  excitation  in  non-curarised  as  in  curarised  muscle.  But 
within  that  range  of  current  intensity,  in  which  the  height  of 
contraction  does  increase  with  the  increment  of  stimulation,  the 
latent  period,  according  to  the  same  author,  steadily  increases 
with  decreasing  height  of  contraction,  at  first  more  slowly,  sub- 
sequently in  increasing  proportions.  This  is  true  of  normal,  as 
well  as  of  curarised,  muscle. 

The  Latent  Period  of  the  Entire  Muscle  and  of  the  Muscle 
Elements 

At  this  point  we  must  attack  the  question  often  raised  in 
recent  discussions,  whether  the  latency  period  of  the  muscle  element 
{i.e.  smallest  section  of  a  primitive  fibre)  differs  or  no  from  that 
of  the  entire  muscle  (consisting  of  many  fibres).  All  the  observa- 
tions, after  Helmholtz,  on  the  time-relations  of  contraction,  refer  to 
individual  muscles  in  the  coarse  anatomical  sense.  But  if  we 
look  more  closely  into  the  mechanical  alteration  in  state  of  the 
muscle  elements  {i.e.  least  possible  segments  of  a  fibre)  it  is 
evident  that  not  only  the  active  changes  in  form  and  constitution, 
produced  by  the  excitatory  processes,  but  also  the  passive  dis- 
position, which  results  from  the  interconnection  of  the  individual 
elements  in  the  continuity  of  the  fibre,  must  be  taken  into  con- 
sideration. To  a  final  theory  of  the  muscular  process  the  former 
only  is  of  immediate  importance,  but  the  other  factors  cannot 
be  neglected,  since,  as  is  easy  to  see,  they  are  essentially 
significant  in  the  mode  of  manifestation  of  the  contraction  of  the 
entire  muscle.  It  is  not  difficult  to  show  that  on  exciting  one 
end  of  a  loaded  muscle  with  parallel  fibres,  the  part  farthest 
from  the  point  of  excitation  will  submit  to  a  considerable 
extension  before  it  goes  into  contraction.  This  is  best  seen 
in  polymerous  muscles  (29).  If,  e.g.,  the  rectus  int.  maj.  of 
the  frog,  which  has  an  oblique  tendinous  intersection  towards 
the  centre,  is  made  to  hang  vertically  with  the  tibial  end  upper- 


74 


ELECTRO-PHYSIOLOGY 


most,  and  provided  with  two  levers,  one  of  which  is  inserted  in 
the  upper  half  of  the  muscle  just  above  the  intersection,  the 
other  in  the  cartilaginous  acetabulum,  and  if  the  lower  half  of 
the  muscle  is  then  excited  with  single  induction  shocks,  the 
graphic  record  of  the  change  in  form  of  both  halves  of  the 
muscle  shows  at  once  that  at  the  moment  when  the  lower  and 
directly  excited  half  begins  to  shorten,  the  upper  remains  pas- 
sively extended  (Fig.  39). 

"  But  the  consequent  rise  of  the  upper  curve  soon  changes 
into  a  fall  below  the  abscissa,  corresponding  with  a  shortening  of 
the  upper  half  of  the  muscle,"  which  is  brought  about  j^cissively 

like  the  previous  exten- 
sion. "  As  soon  as  the 
lower  muscle  contracts, 
its  two  ends  are  drawn 
together,  i.e.  it  raises  the 
weight  on  the  one  side, 
and  extends  the  upper 
half  of  the  muscle  on  the 
other.  But  the  weight, 
once  set  in  motion,  rises 
in  virtue  of  its  inertia 
far  beyond  the  intrinsic 
height  of  lift  ('  height  of 
projection  ').  At  the  same 
moment  the  entire  muscle,  including  the  upper  half,  is  unloaded ; 
the  latter  flies  back,  and  shortens,  thus  simulating  a  natural 
contraction"  {I.e.  251). 

This  phenomenon  was  actually  applied  by  Eegeczy  (30)  in 
support  of  the  view  that  the  excitation  process  passes  from  one 
half  of  the  muscle  to  the  other  by  means  of  a  tendinous  inter- 
section. If  all  jar  is  avoided,  extension  of  the  upper  half  of  the 
muscle  only  will  be  produced  under  uniform  conditions,  persisting 
so  long  as  the  lower  half  remains  contracted.  What  is  here  said 
of  a  polymerous  muscle,  divided  by  a  tendinous  intersection  into 
two  parts,  physiologically  independent  of  one  another,  applies 
equally  to  the  two  halves  of  a  monomerous,  parallel-fibred  muscle, 
e.g.  sartorius,  the  lower  end  of  which  is  loaded  and  excited,  a 
light  lever  being  pushed  through  the  centre  of  the  muscle.  The 
upper  half  of  the  vertically  dependent  muscle  will   always  be 


Fig.  39. — o,  Upper;  w,  lower  half  of  muscle.     (Munzer.) 


CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY 


75 


perceptibly  extended  before  it  begins  to  shorten  (31).  This 
effect  fails  when  the  recording  lever  is  connected  with  the  lower 
end  of  the  muscle,  i.e.  vmder  normal  conditions  of  recording  a 
muscular  contraction.  The  shortening  of  the  entire  m.uscle  is 
not  therefore  preceded  by  any  lengthening  (extension).  Each 
individual  muscle  element  is,  however,  in  the  first  place  extended 
by  the  excitation,  or  contraction,  of  a  distant  spot,  for  the  loaded 
muscle  exerts  a  greater  traction  on  its  point  of  dependence  so 
long  as  it  pulls  up  its  load  in  contracting,  than  during  rest  (Gad). 
It  is  therefore  clear  that  under  these  conditions  the  mechanical 
latent  period  of  the  whole  muscle  must  be  longer  than  the 
mechanical  latent  period  of  the  muscle  element,  and  that  accord- 
ingly the  shortest  latent  period  observed  in  the  whole  muscle 
must  approximate  most  nearly  to  the  true  value  of  that  of  the 
muscle  element.  In  order  to  cut  out  this  delay  in  the  latent 
period  as  far  as  possible,  each  point  of  the  entire  muscle  would 
have  to  be  simultaneously  excited,  which  is  not  the  case  in  any 
form  of  electrical  excitation.  Even  where  current  passes  through 
the  entire  muscle,  the  excitation,  as  will  be  shown,  proceeds  only 
from  given  points  of  the  area  stimulated.  Here,  again,  the 
mechanical  latent  period  represents  only  the  upper  limit  of  the 
true  latency,  since  the  energy  (mechanical  yield  of  work)  of  the 
muscle  must  already  have  exceeded  a  certain  output,  in  order  to 
produce  a  visible  movement  of  the  lever. 

Tigerstedt  {I.e.),  from  a  great  number  of  experiments,  carried 
out  under  most  varied  conditions,  determined  the  following 
values  for  the  mechanical  latent  period  in  the  frog's  gastroc- 
nemius : — - 


Latency  Period  in  Sees. 

No.  of  Experiments. 

Percentage. 

0-003 

1 

1-2 

0-004 

19 

22-1 

0-005 

35 

40-7 

0-006 

24 

27-9 

0-007 

6 

6-9 

0-008 

1 

1-2 

According  to  this  table  the  mechanical  latency  would  be 
from  0-004  to  0'006  sec;  in  most  cases  (41  ° j ^)  it  was  0'005 
sec.  The  mechanical  latent  period  of  the  muscle  elements 
could  certainly  not  exceed  0'004  sec,  but  is  probably  much 
smaller,  since  it  is  certain  that  within  the  time  usually  reckoned 


76  ELECTRO-PHYSIOLOGY 


as  the  latent  period  of  muscular  contraction,  i.e.  between  the 
moment  of  excitation  and  the  estimated  commencement  of  con- 
traction, a  great  number  of  nmscle  elements  must  already  have 
been  thrown  into  mechanical  activity.  Conclusions  as  to  the 
latency  of  muscle  elements  might  with  more  justice  be  deduced 
from  the  latent  period  of  the  exjmnsion  of  a  directly  excited 
point  of  the  muscle,  by  which  the  state  of  activity  of  any 
muscle  particle  can  be  followed  as  it  develops.  A  muscle  element 
is  much  too  small  to  produce  any  perceptible  mechanical  effect 
by  itself  in  contracting,  so  that  the  question  of  the  magnitude  of 
its  mechanical  latent  period  cannot  be  solved  by  direct  experi- 
ment (Gad).  It  may  be  taken  as  proved  by  experiments,  which 
we  shall  discuss  later,  that  there  is  no  latency  period  in  the 
chemical  changes  in  muscle  substance,  consequent  upon  excitation  ; 
whether  there  is  any  appreciable  interval  before  mechanical  energy 
is  locally  developed,  must  be  regarded  as  questionable. 

III. — Effect  of  Loading  (Tension)  upon  Magnitude,  Dura- 
tion AND  Form  of  Muscular  Contraction 

It  has  been  shown  that  the  absolutely  unloaded  muscle  {e.g. 
swimming  in  mercury)  retains  its  contracted  form  if  no  extend- 
ing force  is  acting  upon  it.  It  is  therefore  impossible  to  obtain 
a  graphic  record  of  the  process  of  shortening  and  elongation  in  a 
perfectly  unstretched  muscle.  Some  kind  of  lever,  however 
light,  must  rest  upon  it,  and  the  movements  of  the  lever  are  counter- 
balanced by  a  traction  (load)  working  against  the  shortening, 
as  soon  as  relaxation  commences.  This  entails  certain  errors  in 
the  curve  of  the  contraction  which — particularly  in  the  older 
experiments,  where  inert  masses  were  not  eliminated — have  been 
a  great  source  of  confusion.  More  especially  in  the  descending 
portion  of  the  curve,  secondary  smaller  waves,  with  no  corre- 
sponding active  changes  of  form  in  the  muscle,  are  produced  by 
intrinsic  variations  of  the  rapidly  accelerated  falling  mass. 
At  a  later  period  these  fallacies  were  almost  wholly  avoided  by 
using  the  lightest  possible  lever,  and  choosing  a  suitable  point  of 
attachment  for  the  load  (20).  Where  the  tension  of  the  muscle 
remains  approximately  constant  during  the  course  of  a  contrac- 
tion— as  is  the  case  when  it  is  attached  to  a  long  one-armed 
lever,  of  the  smallest  possible  bulk,  while  a  weight  close  to  the 


CHANGE  OF  FORM  IN  MUSCLE  DUFJNG  ACTIVITY 


77 


fulcrum  pulls  on  the  same  lever  in  the  opposite  direction — such  a 
contraction  is  termed  "  isotonic "  (Fick)  (Fig.  40).  It  will 
then  be  found  as  a  rule  that,  with  heavy  loading,  the  height  of 
such  contractions  decreases  gradually  with  the  magnitude  of  the 
constant  tension,  rapidly  at  first,  and  afterwards  much  more 
slowly,  T)ut  hy  no  means  in  ijro'portion  'with  the  loading,  so  that  the 
corresponding  yield  of  ivorh  increases  simultaneously  without  inter- 
ruijtion  (cf.  Santesson's  tables,  Scandinavischen  Arehiv,  i.  1889,  p. 
25  f.)  Under  certain  conditions  a  direct  increase  in  magnitude 
of  contraction  (height  of  twitch)  is  visible  with  increasing 
tension.      As  early  as   1863,  A.  Fick  observed  in  the  adductor 


Fig.  40.— Isotonic  Method.    (Gad.) 


muscle  of  Anodonta,  which  consists  of  uninuclear  fibre -cells, 
that  the  height  of  lift  increased  wdth  increase  of  loading  ;  Heiden- 
hain  asserted  the  same  paradoxical  fact  in  tetanising  striated  frog 
muscle,  and  later  on  it  was  also  determined  for  single  twitches 
by  different  experimenters,  provided  that  during  the  isotonic 
process  the  load  is  not  excessive  (Fick,  Marey,  v.  Frey,  32). 
More  especially  in  the  case  where  the  tension  of  the  muscle  in 
contraction  increases  constantly,  or  from  a  given  moment  {e.g. 
when  the  muscle  pulls  on  an  elastic  spring),  the  shortening  will 
be  greater  with  stronger,  than  with  diminished,  initial  tension. 
This  fact  was  indeed  established  by  Fick  when  he  showed 
that  if  a  muscle  is  appropriately  hindered  in  shortening,  and  the 


ELECTRO-PHYSIOLOGY 


time  between  stimulus  and  discharge  of  the  muscle  judiciously 
determined,  the  twitch  is  invariably  greater  than  under  normal 
conditions.  The  same  also  appears  when  the  muscle  is  loaded 
with  increasing  weights,  and  discharged  at  the  same  moment  after 
excitation.  Place  (32)  found  that  on  using  a  spring  lever  where 
the  resistance  to  be  overcome,  and  consequently  the  tension 
during  the  course  of  a  contraction,  increases  steadily,  the  height 
of  the  twitch  increases  also  if  the  initial  tension  is  raised  from 
0  to  25  gr.  Tigersted  (26)  subsequently  observed  an  increment 
in  height  of  contraction  with  even  higher  initial  tension,  under 
similar  conditions  ;  and,  lastly,  the  same  relation  is  treated  very 
circumstantially  by  C.  G.  Santesson  (32). 

From  all  these  experiments  we  may  conclude  that  within 
certain  limits  the  magnitude  of  contraction  (height  of  twitch)  in- 
creases along  with  the  initial  tension,  as  well  as  with  augmentation 
of  tension,  during  the  period  of  contraction,  to  which  it  must  be 
added  that  this  increment  in  height  of  twitch' can  neither  be  due 
to  the  mechanical  conditions  of  the  experiment,  nor  to  any 
temporary  alteration  of  excitability  from  the  electrical  stimulus,  but 
must  be  referred  to  a  s'pecific  'proj)erty  of  living  inusde-siibstcmce. 
As  Pick  expressed  it,  the  muscle  is  not  at  a  given  moment  of 
the  twitch  invariably  the  same  elastic  body  possessing  a  given 
(uniform)  tension  in  virtue  of  its  actual  length  at  the  moment. 
The  cause  of  these  manifestations  can  rightly  be  looked  for  in 
nothing  else  than  in  a  latent  state  of  excitation,  produced  by,  and 
varying  with,  the  mechanical  conditions  under  which  the  twitch 
is  consummated.  Schenk  (33),  indeed,  states  boldly  that  the 
strong  reaction  by  which  the  muscle  always  responds  when  its 
contraction  is  in  any  way  inhibited  or  even  hindered,  reacts  upon 
it  again  as  a  "  stimulus,"  which  may  in  its  turn  affect  the  pro- 
cesses both  of  contraction,  and,  under  some  conditions,  of 
resolution  of  contraction  also.  As  a  rule  the  dioration  of  the 
contraction  alters  simultaneously  with  the  height,  on  increasing 
tension  of  the  muscle ;  on  the  other  hand,  the  commencement 
of  shortening  is  not  visibly  affected.  On  raising  the  equi- 
librated mass  to  be  moved  by  the  muscle  to  200  grs.,  Tigerstedt 
found  that  the  latent  period  was  very  slightly  lengthened  in  com- 
parison with  its  proportions  when  only  a  light  lever  of  hardly  any 
bulk  was  carried. 

The  reaction  thus  described  for  the  striated  skeletal  muscles  of 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  79 

Vertebrates  is  by  no  means  confined  to  them,  but  occurs  even  more 
demonstrably  in  smooth,  as  well  as  in  cardiac,  muscle.  We  have 
already  referred  to  Fick's  experiment  of  the  effect  of  increased 
tension  from  increased  loading  on  the  magnitude  of  contraction  in 
the  adductor  muscle  of  Anodonta.  The  consequences  of  augmented 
tension  on  cardiac  muscle  are  very  striking,  both  in  vertebrates  and 
invertebrates.  The  effects  observed  are  indeed  somewhat  ambisu- 
ous,  owing  to  the  intracardiac  nerves,  which,  as  a  rule,  govern  the 
normal  rhythmical  movements  of  the  heart,  and  whose  interference 
is  not  easily  excluded.  The  simplest  experiments  are  those  with 
the  a-ganglionic  ventricle  of  the  frog's  heart,  which  has  been 
separated  from  the  auricle — the  so-called  wpex, — or  with  the  snail's 
heart  [Helix  'pomatia),  where  no  ganglion-cells  have  positively  been 
discovered.  Since  the  apex  of  the  heart — like  all  excised  skeletal 
muscle — contracts  only  on  artificial  stimulation,  otherwise  remain- 
ing permanently  quiescent,  it  is  admirably  adapted  to  experiments 
on  the  effect  of  increased  tension  of  the  muscle- wall,  from  increase 
of  intracardiac  pressure  on  excitability  and  work  yielded.  These 
experiments  were  first  introduced  by  Ludwig  and  Luchsinger  (34). 
In  order  to  isolate  the  pressure  effect  as  far  as  possible,  the  apex 
of  the  heart  was  filled  with  physiological  salt  solution.  Eegular 
rhythmical  pulsations  of  a  ventricle,  which  had  previously  been 
quiescent,  will  usually  begin  at  a  pressure  of  20—50  cm.  of  water. 
A  small  mechanical  stimulus  is  usually  required  to  bring  about  the 
first  contraction,  which  is  then  followed  spontaneously  by  an  entire 
series.  The  pulsation  varies  regularly  with  change  of  pressure, 
and  is  indeed  higher  within  a  certain  range,  in  proportion  with 
the  pressure  (cf  tables  of  Luchsinger,  I.e.  293).  Engelmann 
(35)  made  similar  observations  on  the  equally  a-ganglionic  bulbus 
aortffi  of  the  frog.  The  effect  of  tension  of  the  wall  is,  however, 
seen  most  effectively  in  the  thin- walled  snail's  heart  (36).  Even 
in  the  living  animal,  it  may  be  seen  that  evacuation  of  the  quiescent 
heart,  by  snipping  it,  produces  a  more  or  less  prolonged  pause 
in  diastole,  or  a  much  retarded  action.  If  the  heart  is  excised  it 
is  evident  that  every  expansion  of  the  relaxed  and  empty  ventricle, 
however  slight,  is  sufticient  either  to  set  up  (rhythmical)  contrac- 
tion or  to  accelerate  the  beat  considerably,  so  that  the  force  of 
the  individual  contractions  also  must  be  essentially  augmented. 
The  same  fact  has  also  been  established  by  Schoenlein  (37)  for  the 
heart  of  Aplysia.      When  the  extension  is  not  too  weak,  and  in 


80  ELECTRO-PHYSIOLOGY 


particular  where  it  lasts  for  a  considerable  period,  a  more  or  less 
extensive  after-effect  may  regularly  be  observed — the  rhythmical 
contractions  even  lasting  for  some  time  after  tension  is  removed 
from  the  heart,  Ludwig  and  Luchsinger  observed  the  same  after- 
effect on  the  frog's  heart. 

In  Helix  pomatia  it  is  easy  to  introduce  a  convenient  canula 
through  the  auricle  into  the  upper  part  of  the  ventricle,  and  so 
fill  the  heart  with  fluid  (snail's  blood).  Under  these  conditions, 
the  internal  pressure,  together  with  the  amount  of  wall-tension, 
undergoes  the  simplest  alteration.  It  is  often  sufficient  to  incline 
the  charged  canula,  with  the  heart,  a  little  out  of  the  horizontal, 
apex  downwards,  in  order  to  produce  pulsations  in  the  previously 
quiescent  ventricle.  Another  method,  which  is  in  many  ways  more 
convenient,  is  to  place  the  canula  vertically  with  the  heart,  so  that 
the  pressure  of  the  entire  column  of  fluid  acts  on  the  inner  wall  of 
the  ventricle.  It  is  then  easy  by  gradual  immersion  in  a  second 
vessel,  filled  with  0'5  °/^  salt  solution,  to  raise  the  pressure  acting 
upon  the  external  surface  of  the  heart  from  zero  to  the  point 
at  which  internal  and  external  pressure  are  equal,  and  wall-tension 
therefore  abolished.  The  difference  of  level  of  the  fluid  in  the  tube 
and  in  the  external  vessels  will  then  be  the  measure  of  amplitude  of 
wall-tension  at  any  moment.  The  following  figures  illustrate  the 
changes  of  pulse-rate  with  change  of  wall-tension  under  the  above 
conditions  : — 

Height  of  Pressure. 
(Difference  of  Level  in  Canula  Beats  per  minute, 

and  External  Vessel. ) 

30  mm.  50 

15     .,  36 

8     „  21 

5     „  11 

2     „  0 

30     „  50 

Luchsinger  (28)  has  also  been  able  to  show  in  the  rabbit's 
ureter  the  effect  in  this  smooth,  muscular  organ,  of  wall-tension 
on  contraction  phenomena ;  so  that  in  view  of  all  the  previous 
evidence  we  cannot  doubt  that  increased  tension  increases  the 
yield  of  work,  not  merely  in  striated  skeletal  muscle,  but  in  an 
even  higher  degree  in  the  heart  and  smooth  muscles.  And  this 
increase  is  expressed  not  only  in  an  increment  of  the  individual 
contractions,  but  also  in  the  discharge  or  acceleration  of  rhythmic- 
ally   repeated    contractions,    i.e.    the    augmented    (wall-)    tension 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  81 

does  not  merely  increase  the  excitability,  but  it  also  acts  directly 
as  a  discharging  stimulus.  Heidenhain  showed  for  striated  skeletal 
muscle  that  not  merely  the  mechanical  yield  of  work  (which  is 
essentially  conditioned  by  the  magnitude  of  contraction  or  height 
of  twitch)  increases,  but  that,  generally  speaking,  a  larger  proportion 
of  the  potential  energy  stored  up  in  the  muscle  is  employed,  i.e. 
that  exchange  takes  place  between  the  greater  part  of  the  chemical 
tensions  ;  and  this  has  been  confirmed  by  later  experiments.  But 
when  this  occurs  with  one  and  the  same  strength  of  a  given 
stimulus,  the  cause  must  lie  in  a  change  of  state  in  the  muscle 
itself,  which  might  be  termed  increase  of  excitability.  When  we 
find  that,  beyond  a  certain  point,  expansion,  or  tension,  ^^er  se  may 
act  on  cardiac  muscle  as  a  permanent  stimulus,  inasmuch  as  with- 
out the  addition  of  any  further  stimulus  it  can  discharge  long 
series  of  rhythmical  contractions — while  in  other  cases  an  external 
impact,  a  new  stimulus,  may  also  be  required,  which,  however, 
would  be  inadequate  without  the  simultaneous  extension  of  the 
muscle — it  seems  legitimate  to  refer  the  increase  of  excitability  (of 
which  it  is  usual  to  speak  in  the  latter  case)  to  the  presence  of  a 
permanent  condition  of  excitation,  caused  hy  the  extension-stinudus, 
tut  in  itself  inadequate  to  23roduce  visible  effects  of  stimulation.  From 
this  point  of  view  the  state  of  increased  excitability  of  living 
matter  would  only  gradually  become  distinguishable  from  the 
state  of  excitation.  Later  on  we  shall  encounter  numerous  facts 
which  are  in  favour  of  this  theory. 

When  a  muscle  is  so  heavily  loaded  that  it  is  unable  to  raise 
the  suspended  weight,  the  most  powerful  stimulus  will  fail  to 
produce  any  external  visible  alteration,  while  at  the  same  time  the 
properties  of  the  muscle  are  fundamentally  altered.  In  the  first 
place,  the  elastic  traction  (tension)  of  the  excited  muscle  is  consider- 
ably greater  in  its  initial  length  {i.e.  in  its  unexcited  state)  than  it  is 
in  the  resting  condition,  for  the  true  contraction  first  appears 
in  consequence  of  this  altered  state,  since  the  dependent  load  is 
overcome  by  the  increase  of  elasticity  due  to  excitation.  By  using 
Tick's  method  it  is  possible  to  prevent  a  muscle  from  perceptibly 
altering  in  lenoth,  and  at  the  same  time  to  show  its  actual  tension 
by  a  visible  indication.  This  is  most  simply  effected  by  attaching 
the  muscle  to  the  short  arm  of  a  two-armed  lever,  while  an 
elastic  spring  confines  the  movements  of  the  longer  arm.  If  the 
latter  is  drawn  out  beyond  the  point  of  insertion  of  the  spring, 

G 


82 


ELECTRO-PHYSIOLOGY 


Fig.  41.— Isometric  Method.    (Gad.) 


and  allowed  by  means  of  a  writing-point  to  record  its  movements 
on  a  travelling  surface,  a  curve  will  be  obtained  (with  almost 
total  exclusion  of  change  of  form  in  the  muscle)  which  represents 

essentially  the  increase 
and  decrease  of  tension 
during  contraction,  with 
approximately  constant 
length  of  muscle  (Figs. 
41  and  42).  Such  a 
curve  is  termed  by  Fick 
an  "  isometric  "  curve  of 
contraction,  because  it  is 
recorded  with  uniform 
length  of  muscle,  while 
with  the  usual  "  iso- 
tonic "  method,  on  the 
contrary,  the  tension  re- 
mains approximately 
constant,  and  the  muscle 
contracts  freely.  It  is 
naturally  impossible  to  obtain  a  tracing  of  an  absolutely  iso- 
metrical  muscular  contraction ;  for  if  a  lever  is  to  be  moved, 
and  serve  as  index  of  increasing  and  decreasing  tension,  the 
muscle  cannot  be  stretched  quite  immovably  between  two  points, 
as  would  be  required  in 
absolutely  mathematical 
and  exact  isometry.  The 
force  opposing  the  tension 
is  rather  exercised  by  a 
movable  body,  which  draws 
a  writing-point  nearer  or 
farther,  according  to  the 
magnitude  of  the  tension. 
Yet  this  occurs  in  so 
slight  a  degree  with  Pick's  tension -indicator  that  the  highest 
appreciable  tension-value  in  the  shortening  of  the  muscle  is  only  a 
fraction  of  a  millimeter.  The  tension-values  to  which  a  muscle 
attains  its  contraction  are  under  some  conditions  very  consider- 
able. If  isotonic  be  compared  with  isometric  curves,  described 
by  the  same  muscle  under  uniform  conditions,  we  find  invariably 


Fig.  42. — a,  Isotonic  curve  of  twitch ;  &,  isometric  curve 
of  twitch. 


11  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  83 

that  the  summit  of  the  latter  lies  much  nearer  to  the  initial 
point  than  the  summit  of  the  isotonic  curve,  i.e.,  in  other  words, 
with  constant  length  the  muscle  reaches  the  maximum  of  tension 
much  sooner  than  with  constant  tension  it  reaches  the  maximum 
of  shortening  (Fig.  42). 

IV. — Effect  of  Fatigue  upon  the  Peocess  of  Muscular 

Contraction 

The  most  fundamental  sign  of  distinction  between  living  and 
dead  matter  is  undoubtedly  that  of  Metabolism,  i.e.  chemical 
processes  taking  place  within  the  living  matter.  By  these 
certain  substances  are  produced,  on  the  one  hand,  which  are 
finally  excreted  as  useless  to  the  organism,  while,  on  the  other, 
nutritive  substances  are  taken  up  and  assimilated.  With  Hering 
we  may  call  the  former  process  "  dissimilation,"  the  latter  "  assimi- 
lation." Hering's  conclusions  as  to  these  two  fundamental  pro- 
cesses of  metabolism  are  so  important  to  our  subject  as  to  demand 
a  full  exposition,  and  this  is  best  given  in  his  own  words  (40), 
"  Assimilation  and  dissimilation  must  be  conceived  as  two  closely 
interwoven  processes,  which  constitute  the  metabolism  (unknown  to 
us  in  its  intrinsic  nature)  of  the  living  substance,  and  are  present 
simultaneously  in  its  smallest  particles,  since  living  matter  is  neither 
permanent  nor  quiescent,  but  ever  more  or  less  in  constant  motion. 
It  is  a  fundamental  property  of  living  inatter,  engrained  deeply  in 
its  nature,  to  assimilate  and  dissimilate ;  and  these  processes 
continue,  provided  only  the  essential  conditions  of  life  are  present, 
without  assistance  from  external  stimuli."  In  so  far  as  living 
matter  is  wholly  unaffected  by  the  occasionally  working  external 
stimuli,  Hering  designates  its  assimilation  (A)  and  dissimilation 
(D)  as  "  autonomous." 

"  So  long  as  the  autonomous  D  and  A  are  equal  in  ratio, 
the  state  of  living  matter  cannot  be  altered,  and  it  remains  the 
same  qualitatively  and  quantitatively."  This  state  of  perfect 
equilibrium  between  the  autonomous  D  and  A  is  termed  by 
Hering  "  autonomous  equilibrium." 

"  This  condition  of  living  matter  is  altered  when  any  stimulus 
incites  it  to  active  dissimilation,  which  is  not  balanced  by  equal 
assimilation.  Under  these  conditions  D  is  no  longer  exclusively 
autonomous,  but  is  reinforced  by  outside  factors ;  it  may  there- 


84  ELECTRO-PHYSIOLOGY  chap. 

fore  be  denoted  as  allonomous,  in  distinction  from  the  purely 
autonomous  process.  The  increased  formation  of  D-products^ 
and  corresponding  loss  of  elements  which  were  formerly  an 
integral  part  of  the  living  matter  itself,  and  entered  into  its 
chemical  composition,  produces  intrinsic  alteration  in  the  sub- 
stance in  proportion  with  the  strength  and  duration  of  the  stimulus. 
Hence  at  the  close  of  excitation  the  substance  is  found  to  be 
quantitatively  and  qualitatively  altered." 

If  the  D-process  is  regarded  as  a  function  of  living  matter,  it 
must  at  this  stage  be  designated  as  less  capaUe  of  functioning. 
Since  the  substance  is  altered,  not  merely  qualitatively  but  quan- 
titatively also,  its  state,  after  the  action  of  a  D- stimulus,  as 
compared  with  its  earlier  condition,  may  in  Hering's  terms  be 
denoted  as  "  below  par " ;  obviously,  therefore,  as  soon  as  the 
D-stimulus  begins  to  act,  the  depreciation  of  the  living  matter 
proceeds  pari  pass2c,  increasing  with  the  duration  of  the  excitation. 
The  potential  dissimilation  of  the  substance,  however,  diminishes 
in  the  same  ratio. 

This  accordingly  denotes  that  excitability  diminishes  in  pro- 
portion with  the  duration  of  the  D-stimulus,  or,  as  it  is  usually 
expressed,  the  substance  fatigues  itself  This  indisputable  action 
of  every  D-stimulus  may  be  further  reinforced  in  its  physiological 
effect  by  an  aggregation  of  disintegration,  or  dissimilation,  products, 
which,  beyond  a  certain  limit,  are  in  many  cases  demonstrably 
inimical  to  the  functions  of  the  living  matter. 

The  manifestations  and  laws  of  "  fatigue  "  were  first  investi- 
gated in  cold-blooded  muscle  (excised,  or  in  situ)  by  Kronecker 
(41)  and  Tiegel  (24) ;  in  warm-blooded  muscle  by  Eossbach  (24) ; 
and,  recently,  in  man  by  Mosso  (42).  A  number  of  conclusions 
have  been  reached,  some  at  least  of  which  must  be  quoted. 

Muscular  fatigue  is  indicated  experimentally  by  the  greater 
strength  of  stimulation  required  in  order  to  produce  a  constant 
yield  of  work,  i.e.  same  height  of  lift  in  contraction  as  in  the 
unfatigued  state,  or,  conversely,  by  the  decrease  of  lift,  or  yield 
of  work,  with  constant  stimulation.  If  the  muscle  is  excited 
rhythmically — at  constant  intervals,  with  uniform  maximal  stimuli 
and  resistance — by  single  induction  shocks,  a  double  alteration 
of  the  contraction  curve  is  seen  in  height  and  in  duration. 
Kronecker  found  in  frog  muscle  that  the  lift  diminishes  regularly 
from  twitch  to  twitch,  and  that  by  a  constant  fraction  of  de- 


CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY 


85 


crement.       The   curve    of  faMgue,    i.e.    the   hne   connecting    the 

A 


Pig.  43. — A,  Twitches  of  a  non-curarised  Frog's  gastrocnemius  witli  normal  circulation.  To  show 
acceleration  of  fatigue  with  increased  frequency  of  stimulation.  Tuning-fork,  ^  sec.  (Engel- 
mann.)  B,  Series  of  contractions  of  flexor  muscles  of  finger,  artificially  excited.  The  load 
(1  kgr.)  was  carried  till  the  finger  became  exhausted.    (Mosso.) 


ELECTRO-PHYSIOLOGY 


tops  of  the  single  twitches  (recorded  at  equal  distances  upon  a 
stationary  surface),  is  in  this  case  a  stroAght  line  (Fig.  43,  A  and 
£)  with  direct  excitation  of  the  muscle. 

Excised  muscle  becomes  exhausted  after  a  certain  number  of 
twitches.  According  to  Tiegel,  the  same  thing  occurs  in  curarised 
muscle  that  has  been  freed  from  blood,  on  rhythmical  excitation 
with  siib  -  maximal  induction  currents.  The  first  (20  to  30) 
twitches  of  a  series  are  the  only  exception  to  the  rule  that 
the  extreme  upper  point  of  equidistant  contractions  lies  in  a 
straight  line ;  in  these  the  curve,  instead  of  falling,  rises  in  a 
staircase  {supra).  In  the  case  of  curarised  muscle  with  normal 
circulation,  this  rise  may  extend  over  several  hundred  twitches, 
of  which  over  a  thousand  may  remain  at  the  same  magnitude, 
while  the  rest  sink  slowly  but  continuously  (Tiegel).  Accordingly, 
as  might  be  presumed,  fatigue  proceeds  much  more  slowly  in 
muscle  with  normal  circulation  and  nutrition  than  in  excised 
bloodless  preparations,  and  the  period  of  "  staircase "  increment 
in  the  twitches  is  much  shorter  in  the  second  than  in  the  first 
case.  It  is  remarkable  that,  according  to  Tiegel  {I.e.  p.  18),  the 
curve  of  fatigue  {i.e.  straight  line)  sinks  much  more  rapidly  to 
the  abscissa  {i.e.  makes  a  greater  angle  with  it)  with  sub-maximal 
than  with  maximal  stimuli ;  i.e.  the  muscle  is  more  quickly 
fatigued  by  sub-maximal  than  by  maximal  excitation,  provided 
the  two  kinds  of  stimulus  alternate  regularly  at  short  intervals. 
When  a  muscle  has  yielded  a  series  of  twitches  at  maximal,  or 
sub-maximal,  excitation,  and  the  rhythm  is  changed  to  a  weaker 
stimulus,  returning  immediately  (after  twenty  or  more  twitches) 
to  the  original  excitation,  the  first  contractions  of  the  last  series 
are  invariably  higher  than  the  last  of  the  first  series  (Tiegel). 
The  muscle  apparently  recovers  during  sub-maximal  excitation 
from  the  stronger  (maximal  or  sub-maximal)  stimuli.  The  height 
of  twitch  diminishes  more  rapidly  in  proportion  as  the  excitation 
interval  is  shorter  (Fig.  43,  A),  and  this  law  holds  both  for 
maximal  and  sub -maximal  stimuli  in  curarised  muscle.  In 
muscle  with  normal  circulation  and  nutrition,  there  is  always  an 
interval  between  each  pair  of  stimuli,  in  which  the  height  of 
twitch  does  not  diminish  even  after  protracted  excitation,  and  no 
fatigue  appears  {e.g.  the  beating  heart).  Hence  we  may  assume, 
from  the  previous  observation,  that  during  each  pause  in  stimula- 
tion   the    "  down "    change   caused   by   each    D-stimulus    in    the 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  87 

muscle-substance  is  completely  compensated  by  the  A-process. 
In  other  cases  (with  greater  stimulation-frequency),  it  is  perfectly 
intelligible  that  a  progressive  fatigue  and  decrement  of  the  magni- 
tude of  contraction  must  ensue.  The  only  point  that  is  difficult 
to  elucidate  is  the  initial  staircase  increment  of  the  twitches,  more 
especially  in  excised,  bloodless  muscle,  which  seems  in  direct 
contradiction  with  the  previous  theory.  It  is  clear  that  we 
could  only  come  to  a  right  understanding  of  this  phenomenon 
if  the  A-process,  the  invariable  concomitant  of  the  D-process, 
were  more  taken  into  account  than  has  been  customary  in 
physiology.  There  are  countless  instances  in  which  we  may 
observe  that  living  matter  after  undergoing  the  "  down  "  change 
consequent  on  a  D-stimulus,  i.e.  falling  helow  -par,  returns  from 
this  state  to  the  earlier  at  ixtr  of  autonomous  equilibrium,  which 
"  recovery "  (due  to  preponderance  of  A  over  D)  proceeds  with 
so  much  the  greater  energy  in  proportion  as  the  magnitude  of  the 
"  down"  change,  caused  by  the  preceding  stimulus,  has  been  greater. 

It  is  possible  that  we  have  in  this  the  interpretation  of  the 
fact  mentioned  above,  that  muscle  fatigues  more  slowly  with 
maximal  than  with  sub-maximal  rhythmical  excitation.  In  any 
case,  the  living  matter  alters  after  each  cessation  of  a  D-stimulus 
in  virtue  of  its  inherent  energy,  in  a  sense  inverse  to  its  action 
during  the  stimulus,  i.e.  in  an  "  ascending  "  direction.  The  "  re- 
covery "  of  such  living  substance,  "  fatigued "  by  excitation,  is 
always  an  "  autonomous  ascending  alteration,"  by  which  the 
depreciation  of  matter  is  compensated,  and  it  is  brought  back  to 
'par,  as  previous  to  excitation. 

It  would  further  appear  that,  under  favourable  conditions, 
the  "  down "  change  of  substance  produced  by  a  D-stimulus  is 
followed  by  such  an  energetic  "  up "  change  that  the  much 
accentuated  A-process  becomes  not  merely  at,  but  ahove,  par — 
when  it  is  of  course  succeeded  by  an  augmented  D -excitability. 
Such  a  rhythmical  series  would  denote,  not  that  the  living  sub- 
stance {e.g.  cardiac  muscle)  in  equilibrium,  alternated  regularly  in 
"  up  "  and  "  down  "  changes  between  D  and  A,  when  the  preceding 
"  down "  change  would  be  completely  compensated  during  the 
period  of  the  "  up  "  change, — nor  that  there  was  a  "  down  "  change 
in  the  value  of  the  substance  ("  fatigue  "), — but,  on  the  contrary, 
that  there  was  an  ascending  alteration,  as  expressed  in  increase  of 
capacity  for  work  and  augmentation  of  height  of  twitch  in  the 


ELECTRO-PHYSIOLOGY 


muscle.  From  this  point  of  view  we  are  able  satisfactorily  to 
explain  all  the  preceding  evidence  re  staircase  rise  of  contractions, 
and  to  see  in  it  solely  the  expression  of  a  general  law,  according 
to  which  not  only  the  physiological  capacity  for  work  in  any 
organ  {particularly  in  muscle),  but  also  its  morphological  develop- 
ment, which  to  the  last  degree  is  dependent  upon  nutrition,  are 
conspicuously  promoted  by  regular  activity  (effect  of  practice). 
The  degeneration  of  muscles  which  from  any  cause  have  for  a 
long  time  been  inactive  in  the  body,  the  pronounced  development 
of  the  same  when  in  vigorous  exercise,  afford  sufficient  proof 
of  the  favourable  effect  of  muscular  activity  upon  nutrition. 
This  last  is  mainly  subserved  by  the  regulation  of  the  sivp'ply  of 
arterial  Mood,  as  exhibited  in  vertebrate  muscles,  which  must 
also,  of  course,  to  a  greater  or  less  degree  control  the  fatigue 
effects.  Ludwig  and  Sczelkow  observed  in  1861  that  the 
blood-vessels  of  muscles  tvidened  in  contraction,  so  that  the 
blood  circulates  through  them  more  rapidly,  and  Tiegel  (I.e.  p.  81) 
found  the  same  vascular  effect  in  direct  excitation  of  curarised 
frog's  muscle.  Such  a  muscle  treated  at  regular  intervals  with 
maximal  or  sub-maximal  stimuli  (induction  currents)  grows  more 
and  more  red  in  the  course  of  excitation,  and  may  even  set 
up  extravasculation.  The  long  continuance  of  the  "  staircase " 
rise  in  height  of  twitch  under  these  conditions  must  certainly  be 
referred  partly  to  this  hypersemia ;  but  we  have  already  pointed 
out  that  this  is  not  its  sole  cause,  as  is  self-evident  from  its 
appearance  in  bloodless  preparations. 

The  effect  of  fatigue  is,  as  we  have  stated,  not  merely  to  alter 
the  height  of  the  contraction  as  described,  but  also  its  time- 
relations,  which  with  progressive  fatigue  become  more  and  more 
extended.  This  retardation  of  the  course  of  the  twitch,  which 
increases  gradually  during  a  long  series  of  contractions,  and 
expresses  itself  more  particularly  by  a  considerable  extension  of 
the  phase  of  relaxation  of  the  muscles,  may  finally  attain  such 
proportions  that  even  with  longer  intervals  of  stimulation  lasting 
for  several  seconds,  the  muscle  has  not  time  to  relax  to  its 
original  length  before  the  beginning  of  the  next  contraction,  and 
thus  the  base  points  of  each  individual  curve  rise  higher  and 
higher  above  the  abscissa.  Funke  (43)  has  recorded  cases  in 
which  the  myogram  at  the  later  stages  of  fatigue  resembled  a 
steady  tetanus  curve,  although  the  stimulation  intervals  lasted 


CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY 


89 


several  seconds.  But  the  curve  of  contraction  in  fatigued  muscle 
is  not  merely  characterised  by  greater  or  less  extension ;  its  form 
also  is  modified,  especially  in  the  descending  portion.  Generally 
speaking,  this  change  may  be  defined,  with  Fvmke,  by  saying 
that  the  descending  portion  of  the  curve  gradually  loses  its 
character  of  a  free  fall,  owing  to  the  resistance  engendered 
by  fatigue  and  increasing  with  it,  on  which  the  lengthening  of 
the  muscle  is  more  and  more  retarded,  and  always  in  earlier 
stages,  by  the  weight  raised  by  its  own  gravity.  In  the  end,  as 
Funke  has  aptly  expressed  it,  the  muscle  resembles  a  viscous, 
doughy  mass,  responding  with  the  utmost  inertia  to  the  traction 
which  endeavours  to  bring  it  back  to  its  original  dimensions. 
The  ascending  portion  of  the  curve,  on  the  other  hand,  loses  little 
of  its  steepness,  even  when  fatigue  is  carried  to  exhaustion.  The 
shorter  the  intervals  between  the  single  twitches,  the  more  rapid 
will  be  not  merely  the  diminution  in  contraction  magnitude, 
but  also  the  extension  and  change  of  form  in  the  curve  as 
described  above.  In  individual  cases,  the  stage  of  relaxation  in 
otherwise  normal,  non-fatigued,  striated  muscle  is  conspicuously 
lengthened,  so  that,  as  first  described  by  Kronecker  (44)  and 
subsequently  investigated  by  Tiegel  (45),  the  muscles  may  remain 
considerably  shortened  during  long  pauses  (up  to  10  sec.)  in 
a  rhythmical  series  of  simple  induction  shocks.  It  is  evident 
that  this  phenomenon,  which  Tiegel  terms  "  contracture,"  can 
have  nothing  to  do  with  fatigue,  since  with  increased  function  of 
the  muscle  it  diminishes  instead  of  increasing.  In  this  condition, 
which,  as  Tiegel  found,  is  only  developed  in  direct  muscular 
excitation,  the  excitability  of  the  muscle  to  normal  stimulation 
vid  nerve  is  minimal,  while  the  contracture  may  correspond 
with  the  height  of  the  twitch.  The  muscles  of  spring-frogs  seem 
especially  prone  to  contracture,  which  then  appears  even  with 
unimpaired  circulation,  and  is  the  more  marked  in  proportion 
with  the  intensity  of  excitation  (cf  also  Mosso,  I.e.) 

The  course  and  process  of  the  manifestations  of  fatigue  must 
obviously  be  in  the  highest  degree  susceptible  to  all  those  data 
on  which  depend  the  assimilation,  or  dissimilation,  of  muscle- 
substance.  Here,  in  the  first  place,  we  must  consider  the  original 
physiological  condition  in  which  the  muscle  begins  its  fatigue- 
task,  the  widely  varying  range  of  its  "  capacity  for  work "  and 
"  excitability  "  in  normal  connection  with  the  organism,  or  after 


90  ELECTRO-PHYSIOLOGY 


separation  from  it.  We  learn  from  experiment  that  every  muscle 
which  is  excised  and  therefore  deprived  of  normal  conditions 
of  nutrition,  will  sooner  or  later  lose  its  excitabihty  and  become 
moribund.  The  interval  at  which  this  occurs  is  very  unequal  in 
different  animals,  even  in  the  muscles  of  the  same  animal  it 
varies  considerably  with  external  conditions.  In  any  case  we 
must  assume  that  the  autonomous  equilibrium  of  the  muscle- 
substance  is  permanently  disturbed  from  the  moment  of  its 
separation  from  the  organism,  since,  in  consequence  of  the  less 
favourable  conditions  of  assimilation  with  prolonged  dissimilation, 
a  constantly  increasing'  autonomous  "  down "  change  ensues,  as 
expressed  in  diminished  excitability.  As  a  general  rule,  we  find 
that  the  muscles  of  cold-blooded  animals  preserve  their  excita- 
bility longer  than  those  of  warm-blooded  animals,  in  consequence 
of  their  lower  intensity  of  metabolism ;  yet  this  law  is  by  no 
means  universal.  The  muscles  of  fishes,  for  instance,  seem  to 
lose  their  excitability  very  quickly  when  separated  from  the 
organism  (46).  The  expression  "  cold-blooded'"'  further  in- 
cludes the  Invertebrates,  many  of  which  {e.g.  insects)  possess 
muscles  that  perish  very  rapidly.  It  is  noticeable  that  the 
muscles  of  the  same  animal  do  not  all  become  moribund  and  lose 
their  excitability  with  equal  rapidity.  If  the  sarcoplasm  really 
posseses  a  nutritive  function,  as  was  shown  above  to  be  very 
probable,  we  might  expect  that  the  sarcoplasmic  dark  muscles 
would,  as  a  rule,  be  fatigued  and  die  less  quickly  than  the 
a-sarcoplasmic  clear  muscles.  According  to  Grlitzner's  obser- 
vations this  actually  is  the  case.  Eanvier  observed  long 
ago  in  the  triceps  humeri  of  rabbit,  which  consists  of  pale 
(clear)  and  red  (dark)  fibres,  that  it  responds  at  first  like  a  pale 
muscle  owing  to  the  lesser  excitability  of  the  white  fibres,  but 
when  fatigued  with  prolonged  excitation  it  contracts  like  a  red 
muscle,  because  the  white  portion  is  fatigued,  while  the  red  is 
still  capable  of  serving.  This  difference  also  comes  out  very 
clearly  in  the  fact  that,  according  to  Bierfreund  (47),  pale 
muscle  falls  into  rigor  mortis  much  more  quickly  than  red  muscle. 
Under  the  same  conditions  the  first  becomes  rigid  in  1  —  3 
hours,  the  latter  only  in  11—15  hours  after  death.  And  when 
the  rigor  of  the  pale  muscles  has  already  passed  off  again 
completely  (10  —  14  hours  after  death),  the  red  muscles  have 
not  begun  to  lose  their  rigidity. 


II  CHAI^GE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  91 

Finally,  we  have  the  observations  of  Eollett  (48)  on 
the  very  different  contraction  curves  exhibited  by  Dytiscus  and 
Hydrophilus.  The  fresh  muscle  of  Dytiscus  far  exceeds  that  of 
Hydrophilus  in  regard  to  rapidity  and  energy  of  single  twitches, 
but  with  prolonged  activity  the  energy  of  its  contractions  soon 
gives  way,  and  this  is  in  a  much  more  marked  degree  than  their 
rapidity,  although  the  latter  also  diminishes  considerably.  The 
more  sluggishly  contracting  Hydrophilus  muscle,  on  the  other 
hand,  maintains  its  energetic  twitches  at  a  comparatively  high 
level,  even  after  prolonged  activity ;  in  the  process  of  fatigue, 
however,  they  become  more  and  more  extended,  so  that  their 
duration  may  finally  last  twenty  times  longer  than  the  contraction 
of  fresh  muscle. 

As  was  said  above,  the  muscle  -  fibres  of  the  heart  are 
distinguished  by  abundance  of  sarcoplasm,  which  may  well  be 
connected  with  their  extraordinary  vitality  in  many  cases. 
Panum  observed  rudimentary  pulsations  of  the  heart  in  rabbit 
up  to  15|-  hours,  Vulpian  in  the  mouse  to  46,  in  the  dog  to 
9  6  hours,  after  death  (!).  Single  fibres  of  the  cardiac  muscle 
of  mammals  examined  in  physiological  salt  solution  will  often 
exhibit  unmistakable  rhythmical  pulsations  the  day  after  death 
(Sigm.  Mayer). 

In  all  these  cases,  temperature  exerts  the  greatest  influence 
upon  the  total  duration  of  existence,  or  the  steepness  of  decline 
of  excitability,  both  in  isolated  muscle  and  in  the  still  living 
animal.  This  is  intelligible  when  we  remember  the  great 
significance  of  temperature  for  the  intensity  of  all  processes  of 
metabolism,  and,  in  particular,  for  that  of  autonomous  dissimila- 
tion. We  should  therefore  expect  a  priori  that  the  death  and 
corresponding  decline  of  excitability  would,  as  a  rule,  occur 
more  rapidly  with  high  than  with  low  temperature.  The  effect  of 
temperature  is  more  positively  marked  in  cold  than  warm- 
blooded animals. 

Du  Bois-Eeymond  has  found  gastrocnemius  and  triceps 
muscles  of  frog  that  were  still  excitable  at  0°  C.  ten  days  after 
excision,  while  on  a  hot  summer  day  excitability  will  disappear 
after  24  hours,  and  with  medium  temperature  at  about  the  third 
day.  The  data  in  this  respect  are  insufficient  in  regard  to  skeletal 
muscle  in  warm-blooded  animals.  On  the  other  hand,  there  are 
interesting  observations  on  mammals  as  to  the  extraordinary  re- 


92  ELECTRO-PHYSIOLOGY  chap. 

tardation  of  death  by  previous  protracted  cooling  (artificial  cold- 
bloodedness), which  can  be  produced  either  by  dividing  the  spinal 
column  high  up  (Bernard),  or  by  irrigating  the  skin  of  the  belly 
with  cold  salt  solution.  In  rabbits  cooled  in  this  way  to  20°  C. 
in  6—10  hours,  the  direct  muscular  excitability  persists  for  6—8 
hours  after  death  (Israel,  49). 

There  can  be  no  doubt  that  the  immediate  cause  of  death  in 
excised  muscle  is  the  interruption  of  the  nutritive  stream,  and  of 
the  circulating  blood  in  particular.  Even  in  the  living  animal, 
interruption  of  circulation  in  a  muscle,  or  group  of  muscles, 
produces  paralysis  in  a  short  time,  and  eventually  rigor.  This 
experiment  is  only  partially  successful  in  cold-blooded  animals, 
because  their  muscles,  e.g.  in  Amphibia,  though  also  dependent  on 
the  circulation,  exhibit  the  effects  of  ansemia  at  a  relatively 
much  later  period  (Kiihne,  50).  The  muscles  of  frogs  are 
known  to  remain  excitable  for  days,  when  all  the  blood  has  been 
driven  out  by  injecting  the  vessels  with  0*6  ° j ^  salt  solution 
(salt  frogs).  On  the  other  hand,  the  striated  muscles  of  warm- 
blooded animals,  especially  of  birds,  are  correspondingly  more 
sensitive,  losing  their  excitability  after  a  comparatively  short 
time,  and  finally  becoming  rigid  (Schiffer,  51)  when  the  circula- 
tion is  completely  interrupted.  It  is,  however,  possible  to 
restore  or  preserve  excitability,  when  reduced  or  abolished  by 
ansemia,  by  artificial  transfusion  of  arterial  blood.  The  time  up 
to  which  this  will  succeed  after  loss  of  excitability  is  longer  in 
proportion  to  its  normal  persistence  (Brown-Sequard,  46).  The 
excitability  of  smooth  muscles  in  warm-blooded  animals  is  much 
less  dependent  upon  the  circulation,  and  they  are  in  this  respect 
more  like  the  striated  muscles  of  cold-blooded  animals. 

Many  unjustifiable  assertions  have  been  made  with  regard 
to  the  rapidity  of  death  in  smooth  warm-blooded  muscles,  and 
their  sensibility  to  alterations  of  metabolism,  because  the  spon- 
taneous movements  of  certain  smooth  muscular  organs  {e.g. 
intestine)  cease  very  soon  after  death,  and  along  with  them 
excitability  to  artificial  stimuli.  But  it  may  easily  be  shown 
that  this  seemingly  permanent  loss  of  excitability  is  really 
only  produced  hy  cooling,  and  that  the  sensibility  to  stimula- 
tion makes  its  appearance  again  when  the  temperature  is  raised 
artificially  (Biedermann,  52).  The  muscular  wall  of  the  excised 
intestine  of  mammals   retains  its  vitality  in   a  most  surprising 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  93 

manner,  and  has  been  found  excitable  even  more  than  12  hours 
after  death.  So,  too,  the  ureter  of  the  rabbit  or  guinea-pig  will, 
even  after  long  immersion  in  cold,  physiological  salt  solution,  or 
when  taken  from  an  animal  some  hours  after  death  (no  trace  of 
excitation  being  left  under  natural  condition),  become  once  more 
fully  excitable  if  warmed  to  the  body  temperature  {I.e.  387). 
A  similar  tenacity  of  life  was  found  by  Grlinhagen  and  his  pupils 
in  the  sphincter  iridis  of  different  mammals  (53).  Yet  more 
resistant,  according  to  Sertoli  (54),  are  the  equally  smooth 
retractor  penis  muscles  of  certain  mammals  (horse,  ass,  dog), 
in  which  excitability  continues  for  as  much  as  seven  days 
after  extirpation.  During  the  greater  part  of  this  time  the 
muscle  was  in  a  temperature  of  5°— 8°  C,  and  at  the  time  of 
the  experiment  was  only  warmed  to  30°— 37°  C.  If  the  tempera- 
ture remains  at  uniform  height  (39°— 40°)  the  excitability  dis- 
appears in  a  short  time. 

The  rapid  fatigue  of  certain  smooth  muscles  under  perfectly 
normal  conditions  is  in  striking  contrast  with  this  great  capacity 
of  resistance  to  ordinary  nutritive  influences.  •  Engelmann 
{Pfiilger's  Arch.  vol.  ii.  p.  263  f.)  pointed  out  the  effect  of 
fatigue  in  the  rabbit's  ureter  after  every  individual  contraction, 
mechanical  excitability  being  nil  immediately  after  each  twitch 
has  completed  itself.  During  the  subsequent  pause  it  is  gradu- 
ally recovered.  In  a  warm,  fresh  rabbit's  ureter,  where  the 
blood  is  still  normally  circulating,  the  initial  height  of  excita- 
bility is  recovered  after  a  few  seconds.  In  the  rat  even  one 
second  is  not  required  under  the  same  favourable  conditions. 
In  cooled  ureter,  withdrawn  from  circulation,  excitability  returns 
much  more  slowly  and  imperfectly  after  contraction  (5,  10,  or 
more  sees.) 

Thus  we  see  that  excised  muscles  of  cold-blooded  (inverte- 
brate and  poikilothermic)  animals  usually  become  fatigued,  and 
die,  more  slowly  than  those  of  warm-blooded  animals ;  yet  this  is 
by  no  means  an  invariable  rule,  for,  on  the  one  hand,  there  are 
muscles  of  cold-blooded  animals  which  lose  their  excitability 
quickly  even  at  a  low  temperature  (fishes,  insects),  while,  on  the 
other,  certain  smooth  muscles  of  the  warm-blooded  animals  re- 
main excitable  at  low  temperature  for  an  extraordinary  length  of 
time,  even  when  fully  deprived  of  circulation. 

The  muscular  fatigue  consequent  upon  excitation  is,  as  already 


94 


ELECTRO-PHYSIOLOGY 


28  min. 


indicated,    as    much   the 
effect    of    a    "  down " 
change  in  living  matter, 
caused  by  the  preponder- 
ance of  D  over  A  pro- 
cesses, as  is  the  gradual 
death  of  a  muscle  separ- 
ated from  the  organism, 
or  deprived  of  circulation. 
We  should  therefore  ex- 
pect the   changes  which 
occur  in  the  twitch  (or 
contraction)  in  both  cases 
to  agree  in  all  essential 
points.       Decrease   in 
magnitude  of  contraction 
(height    of    twitch),   and 
elongation  (extension)  of 
the     curve,     appear     in 
either    case    as   distinct- 
ive    features.       This     is 
very     apparent     in     the 
pulsations  of  the  excised 
mammalian    heart    (55), 
when    the    fall    of    tem- 
perature {infra)  plays  an 
important  part  (Fig.  44). 
Although  the  condi- 
tion of  muscular  fatigue 
may    thus     be     referred 
mainly  to   a   preponder- 
ance   of    the    D- process 
over   the   simultaneously 
occurring   A-process,    i.e. 
to   a   diminution    of  the 
store     of     decomposable 
matters,  or   of    chemical 
tension,     we     must     not 
neglect     the    other    and 
important    factor    which 


Fig.  44. — Contractions  of  excised  Rabbit's  heart. 
(Waller  and  Keid.) 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  95 

Eanke  in  particular  has  pointed  out,  i.e.  the  accumulation  of 
certain  disintegration  iiroclucts  (56). 

Any  considerable  aggregation  of  the  so-called  D-products  in 
muscle  can  only  occur  in  preparations  that  are  excised  and  with- 
drawn from  circulation,  and  the  rapid  appearance  of  fatigue  in 
such  a  muscle  must  at  least  in  part  be  due  to  this  factor  also. 
The  restorative  effect  of  transfusion  with  (arterial)  blood  can  only, 
however,  consist  in  a  minor  degree  in  the  elimination  of  the  D- 
products  (CO2,  lactic  acid,  KH^PO^,  etc.),  for  otherwise  a  washing- 
out  of  the  muscle  with  any  indifferent  fluid  {e.g.  physiological 
salt  solution)  would  have  the  same  effect  as  the  infusion  of  blood, 
which  never  is  the  case. 

Unquestionably,  therefore,  the  blood  carries  to  the  exhausted 
or  dying  muscle,  matters  which  are  essential  to  the  restora- 
tion of  its  working  powers.  With  regard  to  the  necessary 
quality  of  the  blood,  we  can  speak  with  certainty  of  a  few 
elements  only — oxygen,  e.g.,  which  is  indispensable  to  the  main- 
tenance of  excitability  and  capacity  of  movement  in  all  living 
substance. 

Owing  to  the  relatively  large  bulk  of  an  excised  cold-blooded 
muscle  it  is  capable  of  little,  or  hardly  any,  physiological  ex- 
change with  the  atmosphere,  which  is  only  possible  on  the  surface, 
and  accordingly  the  presence  or  absence  of  free  oxygen  in  the 
neighbourhood  of  such  a  muscle  exercises  a  negligible  in- 
fluence upon  the  conservation  or  restoration  of  its  excitability. 
In  fact,  Hermann  (4,  p.  132)  finds  that  frog's  muscle  retains  its 
excitability  in  perfectly  indifferent  gases  (N",  H),  and  still  more  in 
vacuo,  as  long  as,  or  longer  than,  it  does  in  the  air.  The  transfusion 
of  nutritive  fluids  containing  oxygen,  on  the  other  hand,  produces 
a  very  different  effect.  In  this  case  a  lively  exchange  of  gases 
goes  on  between  the  blood,  which  circulates  freely  inside  the 
muscle,  and  the  muscle-substance,  and  here  the  beneficial  effect 
of  oxygen  on  excitability  may  be  determined  with  certainty. 
Bichat  was  aware  that  venous  blood  could  not  preserve  muscular 
excitability  as  well  as  arterial  blood,  while  Ludwig  and  Schmidt 
(57)  subsequently  showed  that  the  artificial  circulation  in  warm- 
blooded muscles  of  blood  that  had  been  freed  from  oxygen  had 
no  more  effect  than  if  there  had  been  no  such  circulation ;  the 
excitability  in  fact  disappears  more  quickly  in  some  cases  when  a 
muscle  is  injected  with  venous  blood  than  when  it  is  quite  blood- 


ELECTRO-PHYSIOLOGY 


less — which  is  no  doubt  attributable  to  the  directly  inimical 
action  of  CO^.  Experiments  to  the  same  effect  have  been  made 
with  similar  results  on  the  excised  frog's  heart.  When  the  air  is 
much  attenuated  (under  the  air-pump)  the  spontaneous  pulsations 
cease  after  about  an  hour,  and  the  muscle  loses  its  excitability  to 
artificial  (mechanical  or  electrical)  stimuli.  If  the  air  is 
restored  the  pulsations  begin  again.  Cyon,  Klug,  and  Saltet  (58) 
showed  the  dependence  of  cardiac  movements  upon  the  presence 
of  oxygen  in  the  frog's  heart.  It  was  filled  alternately  with 
serum  containing  0,  and  serum  saturated  with  COg:  regular 
pulsations  occurred  only  with  the  oxygenated  serum.  Want  of 
oxygen  therefore  asphyxiates  the  heart  as  in  ciliated  cells  of 
unicellular  organisms.  This  is  principally  due  to  paralysis  of 
the  cardiac  muscles  from  lack  of  oxygen,  as  witnessed  in  the 
gradual  disappearance  of  the  spontaneous  contractions  of  the 
heart,  together  with  a  corresponding  decrease  in  excitability  to 
artificial  stimuli. 

It  is  highly  probable  that  other  nutritive  matters  carried  by 
the  blood  play  a  similar  part  to  oxygen,  while  equally  the 
elimination  of  other  D-products  besides  CO2  is  essential  to  the 
preservation  of  excitability ;  little,  however,  has  yet  been  done  in 
the  way  of  experiment.  Martins  ascertained  for  cardiac  muscle 
that  serum-albumen  had  a  marked  effect  in  restoring  depressed 
action.  When  0'6  %  ISTaCl  solution  is  circulated  through  a  heart 
that  is  beating  spontaneously,  or  from  artificial  excitation,  the 
pulsations,  at  first  vigorous,  disappear  almost  entirely ;  then,  after 
the  heart  has  been  brought  to  a  stand-still,  and  shows  no  trace 
of  movement  even  with  the  strongest  excitation,  not  merely 
excitability,  but  even  automatic  activity,  will  return  if  blood  and 
serum,  or  even  alkaline  salt  solution  containing  serum-albumen, 
are  run  through  the  heart.  Peptone  and  all  other  albuminous 
bodies  (syntonin,  or  albumen,  casein,  myosin)  fail  to  produce 
this  effect.  The  exhausted  muscle  treated  with  these  remains 
absolutely  unresponsive  with  even  the  strongest  excitation, 
whereas  in  every  case,  after  circulation  of  blood  or  serum,  it 
recovered  its  beats,  or  spontaneous  pulsations.  These  experi- 
ments have  not  yet  been  tried  on  striated  skeletal  muscle. 


CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  97 


V. — Effect  of  Temperature  ox  Muscular  Contraction 

The  vital  manifestations  of  all  protoplasmic  tissues  are  much 
affected  by  the  temperature  of  the  moment.  There  is  a  lower 
limit  of  temperature  for  every  organism,  at  which  life  is  per- 
manently, or  at  least  temporarily,  extinguished,  as  well  as  an 
upper  limit  at  which,  principally  on  account  of  the  coagulation 
of  certain  albumens,  such  a  fundamental  disintegration  of  the 
structure  occurs  that  restoration  of  the  normal  functions  seems 
to  be  impossible.  The  absolute  value  of  temperature  varies 
enormously  in  different  kinds  of  protoplasm,  and  even  apart  from 
the  "  immune "  bacteria,  many  cases  are  known  in  which  the 
movements  of  protoplasmic  structures  have  been  observed  at 
a  temperature  far  above  40°  C.  Within  the  maximum  and 
minimum  range  of  "  obvious  contractility,"  we  may  assume  as 
a  general  rule  that  energy  of  the  movement  increases  with 
increase  of  temperature.  This  holds  for  amceboid  as  well  as 
for  flagellated  and  ciliated  movements,  and  the  various  kinds 
of  muscle  form  no  exception.  But  while  in  the  simpler  forms 
of  mobile  protoplasm  it  is  only  possible  to  determine  the  upper 
and  lower  limits,  as  well  as  the  "  optimum  "  of  temperature  at 
which  spontaneous  movements  of  apparently  unlimited  duration 
reach  their  utmost  rapidity,  in  muscle  we  are  able  to  go  a  step 
farther  in  the  analysis  of  phenomena. 

We  have  already  alluded  repeatedly  to  the  great  influence 
exerted  upon  the  manifestations  of  fatigue  and  death,  by  tempera- 
ture ;  an  effect  denoted  by  increase  of  D-products  with  higher, 
and  a  corresponding  decrease  of  these  at  lower,  temperature. 
Along  with  these  are  certain  changes  in  the  time-relations,  and 
form  and  magnitude  (height)  of  contraction,  which  Gad  and 
Heymans  in  particular  have  recently  been  investigating,  and  which 
may  be  viewed  as  a  specific  effect  of  temperature  (60).  If  a 
striated,  skeletal,  curarised  frog's  muscle  is  properly  cooled,  and 
excited  from  time  to  time  by  an  induction  shock,  it  is  found  in 
the  first  place  that  the  (isotonic)  curves  of  contraction  are  more 
extended  in  proportion  as  the  temperature  is  lower.  Comparison 
of  the  accompanying  curves  (Fig.  45)  shows  that  the  period  of 
rising  energy  in  particular  is  much  elongated,  and  the  steepness 
of  the  ascending  portion  decreases  regularly   in  ratio   with  the 

H 


ELECTRO-PHYSIOLOGY 


approximate  constancy  of  steepness  in  the  descending  jDortion. 
Yet  this  constancy  relates  only  to  a  given  upper  portion  of  the 
curve.  The  final  return  to  equilibrium  occurs  more  and  more 
slowly  with  decrease  of  temperature  (and  contraction  residue). 

There  is  a  marked  difference  in  the  effect  of  cold,  and  of 
fatigue,  with  regard  to  the  time-relations  of  muscular  contraction  : 
on  cooling,  the  descending  portion  of  the  curve  is  as  steep  as,  or 
steeper  than,  the  ascending  portion  ;  but  in  fatigue,  which  equally 
prolongs  the  contraction-process,  it  is  found  by  all  authors  to  be 
less  steep. 

A  second  conspicuous  effect,  overlooked  in  earlier  researches, 
is  the  rise  in  height  of  the  contractions,  visible  within  a  certain 
range,  on  cooling.  The  lift  shows  an  absolute  minimum  near  the 
freezing-point  (of  muscle-substance),  where  no  further  alteration 


Fig.  45. — Schematic  representation  of  isotonic  curves  of  contraction  at  different  temperatures. 
(-5to +42i°C.)    (J.  Gad.) 


in  heig-ht  can  be  observed  on  stimulation,  and  a  relative  mini- 
mum  at  about  19°  C,  from  which  point  it  rises  to  the  absolute 
maximum  at  about  30°  C,  and  the  relative  maximum  at  0°  C. 
The  minimum  duration  of  contraction  coincides  with  the  absolute 
maximum  of  lift,  and  increases  constantly  from  this  point,  with 
falling  temperature,  until  the  contraction  disappears.  The  latent 
period  behaves  like  the  period  of  contraction,  increasing  con- 
stantly with  falling  temperature.  We  have  said  that  an  absolute 
maximum  of  twitch  was  reached  at  about  30°  C. ;  if  the  tempera- 
ture rises  beyond  this,  excitability  and  height  of  lift  decrease 
more  and  more,  while  the  duration  of  contraction  i-emains 
approximately  equal  (Fig.  45,  A). 

At  a  moderate  rate  of  heating  it  is  possible  to  show  that  the 
excitability  of  muscle  to  electrical  stimuli  disappears  almost 
entirely  before  the  appearance  of  contraction  from  heat  rigor. 
With  the  isometric  method  temperature  of  course  produces  the 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  99 

same  effect  on  single  twitches,  as  in  isotonic  experiments.  The 
only  difference  is  in  the  form  of  the  apex  of  the  contraction 
curve.  All  isotonic  curves  are  dome- shaped  at  the  summit, 
i.e.  diminution  of  the  ordinates  begins  directly  the  maximum 
has  been  reached.  In  isometric  curves,  on  the  contrary,  a 
plateau  is  formed  by  the  interval  between  temperature  of  the 
room  and  freezing-point,  at  the  summit  of  contraction,  i.e.  the 
maximum  of  tension  remains  constant  for  a  longer  or  shorter 
time  after  it  has  reached  its  climax. 

These  striking  effects  of  temperature  upon  the  height  and 
course  of  contraction  in  striated  skeletal  muscle  seem  to  indicate 
that  two  different  processes  come  into  play  during  muscular 
activity,  which  are  opposed  to  one  another,  and  are  differently 
affected  by  fall  of  temperature.  Fick  pointed  out  that  a  specific 
(chemical)  process  lies  at  the  root  of  muscular  relaxation, 
essentially  differing  from  and  opposite  to  that  underlying  con- 
traction. The  ordinates  of  the  contraction  curve  are  therefore 
not  proportional  to  the  intensity  of  one  process,  but  express  the 
results  of  two  antagonistic  processes.  Fick  suggests  that  the 
first  of  these  may  consist  in  the  formation  of  a  specific  substance 
(decomposition  of  sugar  into  lactic  acid),  the  second  in  the 
further  disintegration  of  the  resulting  product  (breaking  up  of 
lactic  acid  into  H^O  and  CO.^).  The  acid  produces  a  partial 
coagulation  of  the  contents  of  the  sarcolemma,  which  is 
reduced  again  by  removal  of  the  chemical  causes.  Gad  and 
several  of  his  pupils,  as  also  Schenk,  have  recently  worked  out 
this  idea  and  applied  it  to  the  explanation  of  the  phenomena 
under  consideration  (33).  Here  we  need  only  say  that  the 
same  conclusions  follow  naturally  from  Hering's  general  principle, 
and  that  it  w"0uld  be  possible  to  explain  all  the  phenomena 
observed  on  the  supposition  that  change  of  temperature  exerts  a 
more  depressive  influence  upon  one  of  the  fundamental  processes 
of  metabolism  than  upon  the  other. 

On  the  hypothesis  that  the  active  "  process  of  relaxation " 
in  Fick's  sense  goes  hand  in  hand  with  the  process  of  assimilation, 
some  value  may  attach  to  the  observations  of  Fr.  Schenk  (61), 
i.e.  that  relaxation  occurs  more  slowly  in  proportion  with  the 
scarcity  of  reserve  substances  in  the  muscle.  On  comparing  an 
actively  fatigued  muscle  with  one  whose  excitability  has  been 
depressed  by  irrigating  it  with  a  solution  of  lactic  acid,  w^ithout 


100  ELECTRO-PHYSIOLOGY 


diminution  of  its  store  of  reserve  matters,  it  will  be  found  that 
the  latter  relaxes  more  rapidly  than  the  former.  The  one  hehaves 
to  the  other  as  a  cooled  muscle  to  a  fatigued  muscle. 

There  are  no  satisfactory  observations  as  to  the  effect  of 
temperature  on  magnitude  and  process  of  contraction  in  striated 
warm-blooded  muscle,  but  it  has  long  been  ascertained  for  cardiac 
muscle  both  in  cold  and  in  warm-blooded  animals,  that  the  time- 
relations  of  the  natural  and  spontaneous,  as  also  of  artificial, 
contractions,  are  considerably  retarded  by  cooling,  while  the  con- 
trary occurs  with  rise  of  temperature.  The  mechanical  latent 
period  undergoes  similar  changes,  most  conspicuously  in  the  excised 
heart  of  warm-blooded  animals  (A.  D.  Waller,  55).  While  at 
normal  temperature  (38°— 40°)  the  contraction  apparently  begins 
at  the  moment  of  excitation,  a  latent  period  being  only  perceptible 
on  applying  more  delicate  methods  of  time  -  measurement,  on 
vigorous  cooling  (12°— 0°)  it  may  last  for  more  than  a  second. 
It  is  not  known  whether  with  uniform  stimulation  the  same 
relations  between  temperature  and  contraction-magnitude  obtain 
in  cardiac  muscle,  as  have  been  demonstrated  by  Gad  and 
Heymans  for  striated  skeletal  muscle.  If  the  normal  period  of 
contraction  in  a  muscle  is  very  short,  the  effect  of  falling  tempera- 
ture will  be  well  marked,  and  on  the  other  hand  the  shortening  of 
the  contraction  process  by  warming  is  conspicuous  when  the 
muscle  has  previously  been  yielding  a  sluggish  twitch.  This 
is  most  marked  in  smooth  muscle,  where  the  process  of  contraction 
is  accelerated  in  a  remarkable  degree  by  heating. 

The  behaviour  of  smooth  muscle  -  elements  with  varying 
temperature  exhibits  many  interesting  peculiarities,  mainly 
because  in  many,  perhaps  all  cases,  they  fall  into  a  state  of  more 
or  less  marked  and  permanent  contraction  ("  tonus  ")  independently 
of  the  nervous  system,  the  strength  of  which  is  conditioned  in  a 
marked  degree  by  the  temperature  of  the  moment.  This  is 
emphatically  the  case  in  the  smooth  muscles  of  many  invertebrates, 
as  well  as  in  poikilo thermic  vertebrates.  The  adductor  muscles 
of  the  fresh-water  molluscs  (Anodonta,  Unio),  e.g.,  usually  exhibit 
a  well -developed  tonus,  which  is  certainly  independent  of  the 
central  nervous  system.  By  partially  breaking  up  the  shell  in 
large  specimens  of  Anodonta,  it  is  easy  after  removing  the  other 
soft  parts  to  obtain  a  preparation  which  is  well  adapted  to  all 
kinds  of  excitation  experiments  (Fick,  32  ;  Biedermann,  62).      At 


11  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  101 

first  the  muscle  is  always  so  firmly  contracted,  that  it  not  only 
resists  the  strong  traction  of  the  uninjured  elastic  ligament,  but 
will  even  support  a  weight  of  more  than  20  grs.  without  visible 
extension.  Even  when  the  shells  gape  sufficiently,  after  a  long 
interval,  to  make  effective  excitation  practicable,  the  efforts  of  the 
weighted  muscle  to  shorten  are  still  considerable,  as  shown  by  the 
fact  that  each  decrease  of  its  load  is  followed  by  a  corresponding 
shortening.  Even  after  many  hours  the  presence  of  a  certain 
"  tonus "  may  generally  be  demonstrated.  As  soon  as  the 
insertion  of  the  still  living  muscle  is  freed  on  one  side,  it  con- 
tracts quickly  to  less  than  half  its  length  with  completely  closed 
shell.  In  time,  of  course,  this  tonus  diminishes  slowly.  If 
a  preparation  is  left  for  several  hours  at  medium  temperature, 
the  gradual  relaxation  can  be  easily  determined.  While  at 
the  beginning  it  takes  considerable  force  to  separate  the  two 
halves  of  the  shell,  this  becomes  gradually  easier,  and  after 
several  hours  a  weight  of  hardly  10  grs.  will  sometimes  pro- 
duce almost  maximal  extension  of  the  muscle.  When,  therefore, 
the  elastic  ligament  has  not  been  injured  in  preparation,  the 
shells,  which  were  tightly  closed  at  first,  gape  wider  and  wider, 
because  the  ratio  between  the  tension  in  the  opening  ligament 
and  the  tonic  effort  of  the  muscle  to  contract,  alters  constantly 
in  favour  of  the  former. 

The  decrease  of  tonus,  however,  begins  almost  instantaneously 
if  the  preparation  is  submitted  to  a  higher  temperature  (immersion 
in  H^O  at  about  30°  C),  which  soon  effects  a  considerable  relaxa- 
tion. On  subsequent  cooling  the  tonus  is  only  partially  restored, 
though  in  other  smooth  muscles  it  comes  back  completely  (63). 
Bernstein  recently  investigated  the  effect  of  different  temperatures 
upon  the  muscles  of  the  frog's  stomach,  arriving  like  Griinhagen 
and  Samkowy  (64)  at  precisely  the  same  results  obtained  by 
Biedermann  from  smooth  molluscan  muscle.  Bernstein,  after 
removing  the  mucosa,  took  a  circular  piece  of  the  muscular  layer, 
and  stretched  it  between  two  hoops  in  a  glass  vessel,  the  shorten- 
ing, or  extension,  being  conveyed  to  a  writing-lever  by  means  of 
a  thread  running  over  a  pulley.  The  medium  of  heating  was 
either  physiological  salt  solution,  previously  brought  to  the 
required  temperature,  and  then  poured  into  the  vessel,  or  air 
saturated  with  steam.  When  treated  in  this  way  the  ring  of 
muscle  corresponds  exactly  with  the  adductor  muscle  of  molluscs 


102  ELECTRO-PHYSIOLOGY 


as  described  above.  If  any  considerable  tonus  has  been  induced 
by  the  mechanical  stimulation  consequent  on  removal  of  the 
mucosa,  it  only  yields  very  gradually  at  normal  temperature. 
On  the  other  hand,  the  lever  drops  with  increasing  rapidity  if  the 
temperature  is  raised  about  25°— 40°  C.  If  the  muscle  is 
tetanised  during  this  period,  the  contractions  obtained  are  much 
more  vigorous,  which  is  due  less  to  increase  of  excitability  than  to 
diminution  of  tonus.  Extension  ceases  between  45°  and  50°  C, 
simultaneously  with  excitability,  and  contraction  first  reappears 
at  about  57°  C,  being  then  produced  in  great  measure  by  rigor. 
Here  we  have  the  same  fact  as  that  demonstrated  by  Gad  and 
Heymans  in  striated  muscle,  i.e.  that  excitability  to  electrical 
stimuli  disappears  almost  entirely  before  contraction  occurs  from 
heat  rigor.  Previous  to  this,  every  cooling  of  the  preparation 
had  produced  a  contraction,  i.e.  a  reinforcement  or  restoration  of 
tonus.  Grlinhagen  and  Samkowy  confirmed  the  same  reaction  in 
the  bladder  muscles  of  the  frog,  while,  on  the  other  hand,  many 
smooth  muscles  or  warm-blooded  animals  (sphincter  iridis,  muscles 
of  oesophagus)  exhibit  the  contrary  under  similar  conditions,  con- 
tracting with  warmth,  and  relaxing  when  cooled  again.  It  must, 
however,  be  remembered  that  the  effects  of  warming  or  cooling 
are  essentially  conditioned  by  the  temporary  state  of  the  excitable 
substance,  i.e.  in  the  case  above,  by  the  degree  of  tonus.  This 
again  depends  undoubtedly  upon  the  conservation  of  normal  vital 
conditions,  in  particular  of  normal  temperature.  It  is  therefore 
quite  conceivable  that  the  smooth  muscles  of  warm  -  blooded 
animals  may  sometimes  be  atonic,  when  the  corresponding 
elements  of  cold  -  blooded  animals  exhibited  a  marked  tonus. 
This  may  account  partially  at  any  rate  for  the  contradiction,  in 
the  above  authors,  as  to  the  behaviour  of  smooth  muscle  in  warm 
or  cold-blooded  animals.  It  is  certain  that  in  living  aniinals,  the 
smooth  muscle  of  the  blood-vessels  relaxes  locally  when  sufficiently 
warmed  (application  of  a  heated  body  to  small  exposed  artery), 
and  responds  under  these  conditions  like  the  elements  of  cold- 
blooded animals.  Horvath  (65)  observed  that  the  tracheae  of 
mammals  widened  on  heating  (relaxation  of  muscles),  but  became 
narrow  on  cooling  (contraction  of  smooth  elements). 

Striated  cardiac  muscle  also  falls,  under  some  conditions,  into 
a  state  of  permanent  (tonic)  contraction,  and  then  presents  a  very 
favourable  subject  for  the  study  of  action  of  temperature  upon 


CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  103 


"  tonus."  External  stimuli  are  for  the  most  part  the  immediate 
cause  of  the  latter,  although  a  certain  degree  of  tonus  seems  to 
be  present  under  normal  conditions  without  additional  stimuli. 
We  have  frequently  observed  a  persistent  uniform  state  of  con- 
traction in  the  ventricle  of  the  snail's  heart  {Helix  iDomatia), 
after  a  greater  or  lesser  series  of  regular  contractions  conse- 
quent on  sudden  increase  of  pressure  (Biedermann,  36).  This 
condition  is  invariably  developed  in  the  same  way  in  a  heart 
attached  to  a  canula  and  filled  with  snail's  blood  or  0"5  °/^ 
salt  solution.  The  ventricle  at  first  extends  itself  act  maxi- 
mAtm  under  the  total  pressure  of  the  column  of  fluid  in  the 
canula,  and  empties  again  completely  at  each  systolic  contrac- 
tion, but  it  is  soon  evident  that  the  relaxation  at  diastole  is 
incomplete.  There  is,  so  to  speak,  a  contraction  residue  which 
grows  with  each  successive  contraction,  until  finally  the  heart 
ceases  to  relax,  and  remains  in  permanent  (tonic)  systolic  con- 
traction. The  tonus  may  be  resolved  under  certain  conditions  if 
the  preparation  is  exposed  to  a  higher  temperature,  while  it 
reappears  on  cooling.  This  "  cold  tonus "  apparently  reduces 
much  more  rapidly  on  heating  than  the  "  pressure  tonus."  A 
single,  momentary  immersion  in  warm  salt  solution  usually  suffices 
to  bring  the  contracted  ventricle,  with  a  scarcely  perceptible 
"  latent  period,"  into  the  condition  of  complete  diastolic  relaxation. 

A  question  which  naturally  belongs  here,  relates  to  the  upper 
and  lower  limits  of  temperature  at  which  a  muscle  is,  generally 
speaking,  capable  of  functioning,  or  at  any  rate  can  recover  its 
capacity  to  function. 

There  is  nothing  surprising  in  the  fact  that  muscle,  like 
protoplasm  in  general,  may  be  cooled  to  below  0°  C,  without 
permanent  loss  of  excitability,  for  the  freezing-point  of  the  inter- 
stitial tissue-fluids,  as  well  as  that  of  contractile  substance,  must 
necessarily  lie  below  zero.  But  it  is  difficult  to  say  in  detail 
what  kind  of  changes  the  muscle -substance  undergoes  when  its 
capacity  of  reaction  is  almost  abolished  by  cooling.  At  all  events 
the  intensity  of  metabolism  is  reduced  to  a  minimum.  According 
to  Gad  and  Heymans,  restoration  is  impossible  when  reaction 
ceases  entirely,  upon  which  the  excitable  substance  must  have 
been  injured  intrinsically.  This  may  occur  either  from  its  actual 
freezing,  or  from  mechanical  injury  due  to  the  freezing  of  the 
interstitial  tissue-fluids.      Kiihne  and  Hermann,  and  more  recently 


104  ELECTRO-PHYSIOLOGY 


Preyer,  affirmed  that  hard-frozen  muscles  were  still  able  to  con- 
tract on  thawing,  and  Waller  finds  the  same  for  cardiac  muscle. 
But  in  all  these  experiments  it  is  questionable  whether  the 
contractile  substance  itself,  or  only  the  interstitial  fluid,  freezes. 

VI. — Effect  of  Chemical  Substances  upon  Muscular 

CONTEACTION 

The  normal  manifestations  of  muscular  activity  always  betray 
more  or  less  fundamental  disturbance,  when  the  chemical  relations 
of  the  contractile  elements  undergo  any  material  alteration. 
This  appears  already  from  the  experiments  we  have  been  dis- 
cussing, and  in  this  connection  the  study  of  fatigue  phenomena, 
which  undoubtedly  depend  in  part  on  the  accumulation  of  certain 
disintegration  products,  is  very  instructive.  Without  entering 
into  the  action  of  all  the  many  bodies  whose  effect  on  muscular 
excitability  has  so  far  been  tested,  we  may  quote  some  very 
cogent  facts  that  are  of  importance  to  the  sequel.  In  the  first 
place,  we  must  mention  the  curious  and  striking  antagonism 
in  the  physiological  action  of  the  salts  of  sodium  and  potassium, 
which  are  in  such  close  chemical  affinity.  Weak  solutions  of  ISTaCl 
(0"5  —  0"6  °/o)  have  long  been  employed  where  a  fluid  is  re- 
quired to  preserve  the  striated  and  smooth  muscles,  as  well  as  the 
nerves,  of  vertebrates  for  as  long  as  possible  in  approximately  normal 
conditions.  We  are  so  accustomed  on  the  strength  of  repeated 
experiences  to  regard  "  physiological  salt  solution  " —  the  con- 
centration of  which  must,  of  course,  be  adjusted  to  the  content  of 
salt  in  the  tissue,  and  must  therefore  be  correspondingly  greater 
for  sea-animals — as  a  perfectly  neutral  fluid,  that  it  may  well 
surprise  us  to  learn  from  E.  S.  Locke's  recent  observations  (66) 
that  this  is  only  true  to  a  limited  extent,  even  in  striated  frog's 
muscle.  In  experimenting  with  normal  preparations  of  sartorius, 
and  with  preparations  that  had  been  lying  for  a  long  time  in 
0*6  ° I ^  jSTaCl  solution,  he  found  considerable  differences  in  ex- 
citability and  curve  of  contraction.  Single  induction  currents  of 
great  strength  ("  break "  shocks  in  particular)  sent  through  the 
entire  muscle  produced  in  salt  muscles  "  tetanic  contractions  of 
enormous  height  and  a  duration  of  several  seconds,  after  which  the 
muscle  relaxed  suddenly,  and  showed  only  a  slight  contraction 
residue."      S.  Einger  (67)  had  previously  observed  an  inclination  to 


CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  105 


contracture  in  salted  muscle,  and  found  at  the  same  time  that  it  was 
entirely  abolished  by  adding  one  part  CaClg  to  5000  parts  of  the 
JSTaCl  solution.  Locke  also  observed  that  the  high  tetanic  con- 
tractions described  above  disappeared  after  a  short  time,  if  the 
muscle  giving  this  reaction  was  thrown  into  ISTaCl  solution,  plus  a 
10  ^  saturated  solution  of  CaS04.  Here  it  would  seem  that 
a  0'6  y^  ISTaCl  solution  containing  a  calcium  salt  in  the  right 
proportion  is  more  "  physiological "  than  a  pure  unmixed  solution. 
ISTaCl  solutions  whose  percentage  is  over  or  under  0'5  pro- 
duce much  more  marked  changes  in  the  reactions  of  striated 
(frog's)  muscle.  In  the  first  case,  as  Carslaw  (68)  found  on 
circulating  the  fluid  through  the  vessels  of  the  posterior  end  of 
a  frog,  spontaneous  excitation  phenomena  (tetanic  contractions) 
appear  very  quickly,  and  last  for  several  minutes,  with  inter- 
vening pauses.  Solutions  above  0*7  to  1  ^  ISTaCl  produce, 
moreover,  a  shortening  of  the  muscle,  which  resembles  contracture, 
gradually  increasing  and  diminishing  again  subsequently,  while 
at  2  ^  the  fibrillar  twitches  cease,  and  only  a  slowly  increasing 
crenation,  with  corresponding  loss  of  excitability,  appears  in  the 
muscle.  Previous  to  this  point,  single  as  well  as  tetanic  shocks 
are  accompanied  by  contracture.  We  may  therefore  say  that 
within  certain  limits  of  concentration  the  excitability  of  striated 
voluntary  muscle  is  considerably  heightened,  or  directly  stimulated 
(chemically),  by  ISTaCl  solutions,  while  at  the  same  time  a  marked 
inclination  to  contracture  is  present. 

This  increase  of  excitability,  and  excitatory  action  of  pure 
XaCl  solution,  are  greatly  increased  by  the  addition  of  certain  other 
salts  of  sodium,  in  particular  of  Na.^CO.,.  An  uninjured  frog's 
sartorius  may  be  slightly  excited  when  it  is  dipped  into  pure 
0"6  ^  NaCl  solution,  as  indicated  by  fibrillar  twitches,  but  these 
are  never  of  long  duration.  If,  however,  sodium  phosphate 
(Na^HPO^)  and  a  small  quantity  of  ISTa^CO^  are  added  to  the 
solution  (5  grs.  ISTaCl,  2  grs.  Na.,HPO^,  and  0-4-0 -5  grs.  ISTa.^COg 
to  a  litre  of  distilled  water)  it  will  almost  invariably  be  found 
that  the  immersed  muscle,  after  a  shorter  or  longer  period  of 
rest,  sets  up  rhythmical  activity,  provided  the  temperature  be  not 
too  high  (3°— 10°C.)  (69).  In  most  cases  this  is  first  exhibited 
in  a  quick  succession  of  weak,  insignificant,  and  localised  con- 
tractions, discharged  at  the  same  height  from  a  greater  or  less 
number  of  primitive  fibres.      At  times  these  movements  are  so 


106  ELECTRO-PHYSIOLOGY 


weak  that  they  only  appear  in  a  very  slight,  iDut  unmistakably 
rhythmical,  tremor  of  the  immersed  muscle.  Generally,  liowever, 
these  insignificant  manifestations  are  followed  at  the  same,  or 
other,  points  of  the  fibre  by  stronger  contractions,  with  a  slower 
rhythm,  which  under  some  conditions  cause  the  muscle  to  curve 
round  in  a  semicircle  towards  the  surface  or  border,  or  to  roll  up 
screw -fashion  at  regular  intervals.  For  the  rest  there  seems 
to  be  an  inexhaustible  variety  in  regard  to  the  forms  of  move- 
ment, which  may  be  observed  in  these  reactions  running  parallel 
to,  and  interrupting,  or  not  interfering  with,  each  other,  but  all 
having  in  common  that  at  the  same  point  of  the  muscle,  at  a 
given  time,  there  will  be  uniform  rhythm  of  movement  and  inci- 
dence of  stimulus. 

It  is  by  no  means  unusual,  especially  in  the  later  stages  of  the 
action  of  alkaline  salt  solutions,  to  find  that  for  a  long  time  only 
one  point  of  the  immersed  muscle  continues  in  rhythmical  activity, 
so  that  the  preparation  moves  in  the  same  constant  rhythm  as  a 
beating  heart,  and  this  not  infrequently  gives  rise  to  a  phenomenon 
so  strikingly  like  the  "  periodic  function "  of  the  frog's  heart, 
described  by  Luciani  (70),  that  the  analogy  of  the  two  mani- 
festations is  at  once  apparent.  These  periods  often  occur  suddenly 
and  quite  spontaneously  after  the  preparation  has  pulsated  for  a 
long  time  in  regular  rhythm,  the  regular  sequence  of  beats  being 
interrupted  by  a  longer  or  shorter  interval.  In  other  cases  the 
appearance  of  the  phenomenon  is  indicated  by  the  fact  that  after 
a  long  series  of  pulsations  of  uniform  rhythm,  the  pauses  between 
every  pair  of  beats  become  gradually  longer,  without  in  any  way 
altering  the  quality  of  the  single  contractions.  Finally  there 
comes  a  long  pause,  and  then  a  new  series  of  pulsations,  interrupted 
again  by  a  period  of  rest,  and  so  on. 

At  a  low  temperature  the  play  of  rhythmic  activity  may  often 
be  manifested  for  days.  The  phenomenon  assumes  a  special 
interest  when  it  is  considered  in  connection  with  a  series  of  recent 
observations  by  different  experimenters  upon  the  ventricle  of  the 
frog's  heart,  detached  from  the  auricle. 

Merunowicz,  Eossbach,  Stienon,  Gaule,  Gaskell,  Lowit,  and 
others  have  ascertained  that  the  non-ganglionated  "  cardiac  apex  " 
of  the  frog  may  set  up  regular  rhythmical  activity  when  certain 
chemical  substances  which  supply  the  nutrition  of  the  preparation 
are  added  to  a  0'6  %  iSTaCl  solution  that  is  intrinsically  ineffective. 


II  CiTANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  107 

This  brings  forward  the  question,  which  anatomical  constituents 
of  the  cardiac  apex  are  the  first  to  be  excited.  Here,  again,  the 
muscles  seem  to  be  of  primary  importance,  the  more  so  since 
we  have  shown  that  curarised  skeletal  muscle  is  excited  under 
almost  similar  conditions  into  analogous  rhythmical  activity.  It 
seems  to  be  an  almost  universal  property  of  muscular  substance  to 
fall  under  certain  conditions,  with  all  prolonged  stimuli,  into  a 
state  of  visible  rhythmical  excitation.  Such  a  theory  is  not  only 
supported  by  the  foregoing  facts,  but  by  further  observations  on 
the  rhythmical  excitation  of  the  sartorius  and  cardiac  muscles 
with  the  constant  current. 

Apart  from  the  "  spontaneous "  rhythmical  phenomena  of 
excitation,  called  out  in  striated  muscle  by  dilute  solutions  of 
]S'a2C02,  the  specific  action  of  this  salt  is  also  exhibited  in  a 
striking  increase  of  response  to  artificial  stimuli.  This  is  very 
evident  whenever  a  muscle  that  is  not  too  thick,  e.g.  frog's 
sartorius,  is  treated  wholly  or  partly  with  correspondingly  dilute 
solutions.  We  shall  presently  refer  to  a  very  striking  fact  in 
this  connection,  which  bears  on  the  alteration  in  the  effect  of  the 
constant  current  on  a  sartorius,  half  of  which  is  treated  with 
ISTaoCOg.  But  even  with  localised  mechanical  stimulation,  as  well 
as  with  single  induction  shocks,  or  induced  alternating  currents, 
the  increase  of  excitability  asserts  itself  in  a  conspicuous  increase 
in  height  of  contraction,  or  tetanus  curve,  as  well  as  by  an  aug- 
mented tendency  to  contracture. 

The  stronger  solutions  of  ]SraoS04,  as  also  very  dilute  solutions 
of  NaOH  (in  0-5  %  NaCl  solution),  act  like  NaoCOg,  only  in  a 
less  degree,  so  that  seeing  the  identical  action  of  these  substances 
upon  cardiac  muscle,  we  are  justified  in  speaking  of  a  specific 
effect  of  the  sodium  salts  in  question,  i.e.  the  contractile  substance 
of  striated  muscle  is  so  altered  by  the  presence  of  even  small 
quantities  of  these  reagents,  that  it  is  excited  more  easily,  and 
with  smaller  stimuli,  than  under  normal  conditions.  The  much- 
talked-of  and  frequently- tested  action  of  veratrin — an  alkaloid 
whose  conspicuous  effect  upon  striated  muscle  was  first  discovered 
by  Kolliker,  and  subsequently  investigated  by  Bezold  (71),  Tick, 
Bohm  (72),  and  others — is  to  some  extent  comparable.  While  in 
the  application  of  certain  sodium  salts,  and  of  NagCOg  in  parti- 
cular, it  is  the  increase  of  excitability  towards  all  stimuli  that 
comes    prominently    forward,   in    veratrin- poisoning    the    extra- 


108  ELECTRO-PHYSIOLOGY 


ordinary  prolongation  of  the  contraction  period  (contracture) 
exclusively  arrests  attention.  If  a  frog  is  poisoned  with  sub- 
cutaneous injections  of  1—2  drops  of,  say,  a  0'2  °/^  solution  of 
veratrin,  after  a  short  time  a  marked  disturbance  of  the  normal 
movements  usually  makes  its  appearance  characterised  above  all 
by  rapid  and  vigorous  contractions,  while  the  relaxation  and 
elongation  of  the  muscle,  on  the  contrary,  are  very  sluggish. 
This  is  still  more  plainly  seen  in  experiments  with  isolated  nerve- 
muscle  preparations,  especially  when  the  changes  of  form  are 
graphically  recorded.  While  the  ascending  limb  and  summit 
of  the  curve  betray  no  great  alteration,  the  stage  of  falling 
energy  is  much  protracted,  and  relaxation  may  be  prolonged  over 
many  seconds.  Since  v.  Bezold  determined  these  remarkable 
effects  of  veratrin,  it  has  been  admitted  that  they  are  entirely 
due  to  an  altered  state  of  the  muscle -substance  proper,  and 
depend,  as  Tick  affirms,  in  all  probability  upon  an  "  augmenta- 
tion of  the  excitatory  process  beyond  normal  limits."  In  order 
to  produce  maximal  extension  of  contraction,  it  is  advisable 
to  give  larger  doses  of  the  poison ;  we  have  found  it  convenient 
to  introduce  6  —  7  drops  of  a  1  ^  solution  of  veratrin  acet. 
into  the  posterior  lymph  sac,  killing  the  frog  {B.  towpor^  after 
ten  minutes  at  the  latest.  Seven  minutes  usually  suffice  to 
develop  the  symptoms  characteristic  of  the  poison.  In  the  first 
place  may  be  mentioned  the  more  or  less  pronounced  convulsions 
of  the  posterior  extremities,  which  occur  at  short  intervals,  and 
are  preceded  by  a  general  disturbance  and  spasmodic  gaping. 
One  unmistakable  symptom  is  that  the  muscles  of  the  belly  go 
into  protracted  tetanus  when  mechanically  excited,  e.g.  on  pinching 
with  forceps,  as  also  occurs  in  a  preparation  of  the  sartorius 
when  the  nerve  is  divided.  The  rapid  twitch  at  the  moment  of 
division  is  often  succeeded,  after  a  short  pause,  by  a  further,  slowly 
increasing  contraction,  which  remains  constant  for  some  time, 
and  only  gradually  yields  to  relaxation. 

If  the  changes  of  form  in  such  a  veratrinised  sartorius  are 
recorded,  by  fixing  it  between  the  stumps  of  bone  left  on  either 
side  to  Bering's  double  myograph  (which  will  be  described  below), 
one  of  the  two  movable  non-polarisable  electrodes  having  pre- 
viously been  fixed  permanently,  the  same  curves  are  usually 
obtained,  whether  the  excitation  is  produced  by  an  induction 
shock  sent  into  any  part  of  the  muscle,  or  by  minimal  closure  of  a 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  109 

battery  current.  In  either  case  the  waves  of  contraction  are,  as 
it  were,  fixed  in  their  passage  through  the  muscle,  and  a  more  or 
less  prolonged,  nearly  uniform  tetanus  ensues,  or,  as  it  is  better 
expressed  in  the  absence  of  almost  any  evidence  of  discontinuity 
in  the  contraction,  there  is  a  "  tonic  "  shortening  in  all  the  parts 
of  the  entire  muscle. 

As  already  shown  by  Bezold  and  Fick,  different  forms  of 
contraction  may  be  distinguished  in  the  veratrin  muscle,  one 
of  the  commonest  being  that  in  which  the  peculiar  tonic,  per- 
sistent contraction  is  preceded  by  a  more  or  less  pronounced 
and  rapid  introductory 
twitch.  As  shown 
above,  there  is  a  rapid 
maximum  contraction  at 
the  moment  of  excita- 
tion, followed  immedi- 
ately by  a  considerable 
extension,  succeeded  in 
its  turn  by  a  second 
slow  contraction  which 
only  gradually  yields 
to  relaxation  (Fig.  46). 

Indications  of  this     ^  ' 

characteristic     contrac-    /ududuU\-U^AjiJy-JUiXjU^^Ajd^..J^uU\ 

tlOn  are  rarely  absent,  pio.  46.— Make -twitch  of  veratrinised  Frog's  sartorius  (1 
eSDeciallv  if  the  nremr-  Danlell).    The  characteristic  tonic  contraction  is  preceded 

.  .  Jr      r  ^y  ^  rapid  initial  twitch.     (Biedermann.) 

ation  is  immersed  for  a 

long  period  in  dilute  salt  solution.  As  Fick  showed,  the  initial 
twitch  cannot  be  explained  by  indirect  excitation  of  the  muscle  from 
the  intra-muscular  nerves — the  subsequent  persistent  contraction 
only  being  due  to  direct  excitation  of  the  muscle — for  the  same 
curves  are  exhibited  after  previous  curarisation.  The  phenomenon 
may  presumably  be  related  to  the  fact  first  observed  by  Griitzner, 
of  the  constitution  of  muscle  out  of  two  morphologically  and  func- 
tionally different  kinds  of  fibres,  corresponding  to  the  red  and 
pale  (sluggish  and  quick)  muscles.  This  view  receives  support 
from  the  fact  that  the  same  double-topped  curves  of  contraction 
are  not  infrequent  under  other  conditions,  e.g.  local  treatment 
with  NaoCOg,  or  even  in  perfectly  normal  frog's  muscle.  In 
sartorius  itself  Griitzner  finds  it  to  be  the  rule.      If  the  veratrin 


no  ELECTRO-PHYSIOLOGY 


muscle  is  repeatedly  excited  during  the  stage  of  relaxation  by  a 
short  closure  of  the  constant  current,  its  response  to  the  make 
excitation  will  generally  be  less  in  proportion  to  the  height  of 
its  contraction  during  the  previous  stimulation.  It  not  infre- 
quently happens  that  the  muscle,  even  when  fully  relaxed,  will 
hardly  give  any  perceptible  response  to  the  same  stimulus  that 
recently  elicited  a  marked  contraction.  But  in  the  majority  of 
cases  the  increment  of  excitation  effects  proceeds  "pari  'passu  with 
the  progressive  relaxation  of  the  muscle,  so  that  the  twitches 
served  up  during  the  latter  period  at  equal  intervals,  and  of  very 
brief  duration,  all  rise  to  a  uniform  height  above  a  line  of  abscissa 
— corresponding  with  the  descending  portion  of  the  curve  traced 
by  the  muscle  after  a  single  excitation.  Tick  made  similar 
observations  with  indirect  excitation  {vid  nerve)  of  a  veratrinised 
frog's  muscle  (*72,  p.  146). 

As  we  have  said,  the  character  of  the  twitches  alters  in  a 
marked  way  with  rapidly  repeated  excitation,  relaxation  soon 
occurring  as  quickly  as  under  normal  conditions.  If  the  muscle 
is  left  for  some  time  unexcited,  the  first  renewed  contraction 
again  exhibits  all  the  characteristic  veratrin  effects.  Temperature 
is  an  important  factor,  since  the  typical  contraction-curve  of  the 
veratrin  muscle  is  most  pronounced  at  medium  temperature,  and 
less  characteristic  alike  in  great  heat  and  in  cold.  In  both  these 
cases  (Lauder-Brunton  and  Cash,  73)  the  phenomena  of  veratrin 
contracture  disappear,  to  return  again  when  the  cooled  or  heated 
muscle  is  restored  to  a  medium  temperature.  But  the  recovery 
is  not  invariable,  so  that  it  would  appear  as  though  the  veratrin 
effect  can  be  permanently  abolished  by  change  of  temperature. 

Barium,  salts  act  like  veratrin  upon  the  substance  of  striated 
muscle,  while  the  potassiuni  salts  in  general  act  as  a  muscle 
poison,  depressing  excitability  more  or  less  quickly,  and  finally 
abolishing  it.  This  is  to  a  marked  degree  the  case,  even 
with  highly  dilute  solutions,  so  that,  as  indicated  by  Eanke, 
the  salts  of  potassium  presumably  play  an  important  part  among 
the  "  fatigue  products  "  of  muscle.  It  is  certain  that  both  with 
localised  applications  of  K  salts,  and  on  circulating  them  in 
solution  through  the  muscle,  every  characteristic  manifestation 
of  muscular  fatigue  is  produced,  which  can  again  be  entirely 
cancelled  by  simply  washing  out  the  preparation  with  0'6  % 
NaCl  solution. 


13. 


CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  111 


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VII. — Summation  of  Stimuli  and  Tetanus 

We  have  so  far  been  considering  single  twitches  only,  as 
yielded  when  a  muscle  is  excited  by  stimuli  of  short  duration. 
It  remains  to  be  seen  how  a  muscle  reacts  when  two  or  several 
stimuli  succeed  each  other  at  diminishing  intervals.  If  the 
pauses  are  long  enough  to  allow  the  muscle  to  relax  completely 
before  the  commencement  of  each  new  contraction,  a  series  of 
twitches  is  produced,  in  which  each  is  completely  separated  from 
the  others,  and  only  affected  indirectly  (as  in  the  staircase,  or 
fatigue)  in  regard  to  magnitude  and  process  of  contraction.  But 
if  the  intervals  are  lessened,  and  the  stimuli  (single  induction 
shocks)  succeed  each  other  more  rapidly,  a  limit  will  soon  be 
reached  at  which  the  new  stimulus  begins  to  take  effect  before 
the  first,  or  subsequent,  twitches  are  completed,  so  that  the 
muscle  is  hindered  from  ever  returning  to  perfect  relaxation. 
There  will  thus  be  a  certain  contraction  remainder,  which  is  in 

I 


114  ELECTRO-PHYSIOLOGY 


ratio  with  the  stimulation  frequency,  and  at  which  the  muscle  in 
a  measure  oscillates.  The  more  rapid  the  sequence  of  stimuli,  the 
more  tense  will  be  the  contraction  of  the  muscle,  and  the  smaller 
the  individual  rhythmical  oscillations,  which  finally  betray 
themselves  only  by  a  slight  irregularity  of  the  "  tetanus  curve  " 
in  a  tracing,  or  to  the  eye  by  a  slight  tremor  of  the  shiny 
surface. 

Finally  this  "  incomplete  "  fuses  into  "  complete  "  tetanus, 
in  which  visible  changes  of  form  can  no  longer  be  detected. 
The  muscle  reaches  its  maximum  of  contraction  soon  after  the 
commencement  of  the  tetanising  excitation,  and  the  summit 
usually  lies  in  this  case  much  higher  than  in  the  (maximal) 
single  contractions ;  during  the  persistence  of  the  intermittent 
excitation  it  remains  uniformly  contracted,  and  returns  rapidly 
to  rest  (as  a  rule)  when  this  is  over.  In  spite  of  its  apparent 
steadiness,  tetanus — as  follows  directly  from  its  origin — must  be 
regarded  as  a  discontinuous  process,  arising  out  of  a  summation 
of  single  twitches,  which  are  only  prevented  by  the  sluggishness 
of  the  muscle  from  expressing  themselves  in  visible  mass-move- 
ments, while — as  we  shall  see — the  internal,  molecular  changes 
do  clearly  and  unmistakably  reveal  their  intermittent  character. 

The  manifold  varieties  of  tetanus  forms  of  contraction  are  only 
to  be  understood  when  the  laivs  of  summation  of  stimuli  under  the 
simplest  conditions  are  familiar  to  us.  Here  again  we  are 
indebted  to  Helmholtz  (1)  for  the  first  fundamental  investiga- 
tion. He  led  two  maximal  induction  shocks  into  the  nerve  of 
a  muscle  in  rapid  succession,  by  opening  two  primary  circuits 
behind  the  same  secondary  coil,  one  after  the  other.  If  the 
second  excitation  fell  in  the  latent  period  of  the  first,  it  pro- 
duced no  effect,  and  the  curve  of  contraction  showed  no  differ- 
ence from  that  traced  by  the  first  alone.  But  if  it  fell  later, 
the  relations  of  the  corresponding  curve  would  be  the  same  as 
if  the  second  stimulus  had  ensued  during  the  resting  stage  of 
the  muscle.  "  From  the  point  at  which  the  second  excitation 
becomes  effective,  the  twitch  behaves  as  if  the  contracted  state 
of  the  muscle  at  the  moment  was  its  natural  state,  and  the 
second  twitch  alone  induced  in  it"  (Fig.  47). 

Let  {a,  h,  ,c)  be  the  contraction  curve  of  the  first  excitation, 
and  (d,  e,  f)  of  the  second,  in  their  separate  working,  then  the 
actual  curve  according  to  Helmholtz 's  law  woidd  correspond  to 


n  ■  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  115 

the  line  {a,  g,  h,  i,  k).  We  can  readily  see  that  the  height .  of 
the  summated  twitches  must  be  greatest,  i.e.  doubled,  when  the 
interval  of  both  stimuli,  like  the  stage  of  rising  energy,  is  a 
simple  contraction.  This  rule  naturally  loses  its  significance  when 
several  uniform  stimuli  follow  successively  at  equal  intervals, 
since  a  maximum  of  contraction  is  soon  reached  and  cannot  be 
exceeded.  On  the  other  hand,  it  is  possible  that  each  individual 
stimulus  in  incomplete  tetanus  may  produce  an  equivalent 
period  of  rising  energy.  V.  Kries,  however,  showed  that  this 
does  not  occur,  even  with  summation  of  only  two  twitches. 
As  is  obvious  from  the  above  scheme,  the  apex  of  the  summated 
curve  must  coincide  with  that  of  the  second  single  twitch,  or  lie 
vertical  to  it,  if  Helmholtz's  law  is  of  general  application. 
According  to  v.  Kries  (2),  however,  this  is  not  the  case.  In 
1886  he  pointed  out  that  in  summated  contractions  the  maxi- 


FiG.  47. — Sclieiua  of  superposition  of  two  twitches.    (Helmholtz.) 

mum  of  shortening  was  reached  much  sooner  after  the  second 
excitation  than  in  a  single  twitch,  i.e.,  in  other  words,  the  period 
of  rising  energy  is  shorter  in  the  second  twitch  than  in  the 
first.  If,  with  V.  Kries,  we  denote  the  interval  at  which  the 
apex  of  the  summated  twitches  succeeds  the  second  stimulus,  the 
"  apex-time,"  and  the  magnitude  of  the  ordinates  of  the  sum- 
mated  twitch  the  "  apex-height,"  we  find  that  (as  above)  in  a 
series  of  "  rising  "  or  "  falling  "  summated  contractions  {i.e.  in  the 
period  of  ascending  or  diminishing  energy),  discharged  by  two 
maximal  induction  currents,  the  "  apex-time "  decreases  with  a 
rising  "  apex-height "  (Fig.  48).  This  is  expressed  in  the  accom- 
panying series  of  curves,  in  which  the  place  of  the  second 
stimulus  remains  unaltered,  while  that  of  the  first  can  be  moved 
to  any  distance ;  the  apex  of  the  summated  twitch  falls  so  much 
farther  from  the  first  stimulus  in  proportion  as  it  lies  higher. 
If  we  compare  a  rising  and  falling  summated  twitch,  it  will  be 
found  that  the  "  apex-time  "  of  the  first  is  higher  than  that  of  the 


116 


ELECTRO-PHYSIOLOG^Y 


second.  The  shortening  of  the  apex-time  is  much  more  obvious 
in  incomplete  tetanus,  when  the  period  of  rising  energy  often 
appears  to  be  reduced  to  the  third  or  fourth  part  of  the  time 
which  it  takes  in  single  twitches. 

Moreover,  we  learn  from  the  relations  of  height  in  a  contrac- 
tion which  is  the  sum  of  two  simple  twitches,  that  the  theory,  by 
which  the  later  of  the  two  is  regarded  as  a  single  contraction 
upon  a  different  abscissa,  is  not  legitimate.      Kronecker  and  Hall 


Fig.  48. — o,  Series  of  ascending ;  6,  series  of  descending  summated  twitches.  The  place  of  the 
second  stimulus  is  the  same  in  both  cases,  and  only  the  first  varies.  The  apex-height  of  the 
summated  twitches  inclines  towards  the  left.    (v.  Kries.) 


(3)  found  the  height  of  "ascending"  maximal  contractions  to  be 
greater  at  first  than  would  correspond  with  Helmholtz's  law,  but 
so  much  the  smaller  afterwards,  accordino;  to  the  degree  in  which 
the  second  contraction  superposed  itself  behind  the  earliest 
twitch.  The  greatest  energy  was  developed  by  the  second 
impulse  when  it  fell  in  the  first  -g-  of  the  primary  curve  of 
contraction.  The  curve  does  not  then  proceed  as  if  the  state  of 
contraction  of  the  muscle  at  this  moment  were  its  point  of  rest, 
the  second  twitch  only  being  excited,  but  the  impulse  of  the  first 
twitch  is  still  effective.      In  the  second  and  third  ^  the  second 


CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY 


117 


twitch  helps  the  first,  pretty  mucli  according  to  Helmholtz's  law, 
while  in  the  case  where  the  second  contraction  rises  from  the 
summit  of  the  first,  the  height  of  the  summated  contraction  is 
always  less  than  would  correspond  with  the  rule. 

We  have  already  considered  the  effect,  where,  on  repeated 
excitation  with  equal,  maximal,  induction  currents,  the  height  of 
twitch  grows  in  the  form  of  a  "  staircase."  The  significance  of 
this  fact  to  the  consequences 
of  summation  has  been 
pointed  out  by  Ch.  Eichet 
(4)  in  particular.  He 
chiefly  investigated  the 
striated  muscle  of  crab, 
in  which  the  increase  of 
excitability  with  repeated 
and  uniform  stimuli  is 
very  marked.  Even  in 
the  case  in  which  the 
single  stimuli  individually 
excite  only  sub  -  maximal 
twitches,  and  exhibit  hardly 
any  perceptible  change  of 
form  (are  "  subliminal "), 
they  may,  on  repeated 
application,  become  effec- 
tive, because  each  single 
excitation  increases  the 
muscular  response  to  the 
next  stimulus  {addition 
latente).  Tig.  49  demon- 
strates   very    forcibly   this 


Fig.  49. — "  Addition  latente"  ;  muscle  of  Crab  ; increas- 
ing effect  of  seven  consecutive  single  stimuli  (induc- 
tion shocks),  each  ineffective  pec  se.    (Ch.  Eichet.) 


effect  of  repeated  uniform  stimuli,  each  ^j)er  se  ineffective,  upon 
the  muscle. 

The  two  first  stimuli  had  no  perceptible  action,  the  third 
stimulus  produces  a  minimal  contraction,  the  fourth,  one  some- 
what greater,  while  the  three  subsequent  stimuli  produce  very 
marked  contractions,  which  are  fused  into  an  incomplete  tetanus. 
It  is  clear  that  such  a  dependence  of  excitability  upon  a  previous 
excitation  must  sensibly  affect  the  height  of  a  summated  twitch, 
as  well  as  the  magnitude  of  the  tetanus  shortenine-.      And  thus 


118 


ELECTRO-PHYSIOLOGY 


it  becomes  intelligible  that  under  certain  conditions  the  height  of 
a  summated  twitch  may  far  surpass  that  of  its  two  components. 

It  was  shown  above  that  the  magnitude  of  interval  between 
each  pair  of  stimuli  must  not  exceed  a  certain  limit,  if  the  bene- 
ficial effect  of  the  preceding  stimulus  is  to  be  observed  upon  its 
successor,  and  it  is  intelligible  that  under  some  conditions  tetanus 
may  be  set  up  in  the  muscle,  in  consequence  of  a  rapid  succession 
of  weak  stimuli,  although  these  in  themselves  would  produce  no 
visible  change  of  form  in  the  muscle.  The  intensity  and 
frequency  of  stimulation  necessary  to  produce  such  a  summation 
(Ptichet's  addition  latente)  must  of  course  depend  upon  the  nature 
of  the  muscle.  As  a  general  rule,  sluggishly  reacting  muscle  is 
more  predisposed   to  summation  of  stimuli  than  quick  muscle, 


Fig.  50. — A,  Simple  twitch  (muscle  of  Crab);  A'^,  summated  twitch,  from  two  closely 
approximated  stimuli  of  the  same  magnitude  as  A.    (Richet.) 


which  tallies  with  the  rapid  expiration  of  all  phenomena  of 
excitation  in  the  latter,  since  the  persistence  of  any  kind  of 
change  in  the  muscle-substance  resulting  from  a  stimulus  is  the 
necessary  condition  of  a  subsequent  heightening  of  excitability. 
The  comparatively  sluggish  striated  muscle  of  the  heart  may  be 
indicated  as  peculiarly  suited  to  summation  effects  in  the  above 
sense.  Basch  (5)  sliowed  that  subliminal,  single,  electrical 
stimuli,  inadequate  in  themselves  to  produce  any  contraction,  will 
gradually  (addition  latente)  increase  the  excitability  of  the  heart- 
muscle  (frog)  if  led  into  it  at  short  intervals,  until  finally  con- 
tractions will  be  discharged.  Engelmann  (6)  made  similar  obser- 
vations on  the  bulbus  aortse  of  the  frog's  heart,  which  also  exhibits 
unmistakable  effects  of  summation  when  rhythmically  excited ; 
the  most  obvious  instances,  however,  are  in  smooth  muscle.      Here 


CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY 


119 


it  often  happens  that  even  with  the  most  favourable  conditions, 
the  strongest  single  induction  shocks  scarcely  produce  any  visible 
effect  of  excitation  (contraction),  while  the  same  parts  (intestine, 
ureter,  muscle  of  mollusc)  are  thrown  into  tetanus  by  the  rapid 
succession  of  stimuli  from  a  vibrating  Neff's  hammer,  at  compara- 


FlG.  52. 


Fig.  53. 


Figs.  51-53.— Muscle  of  Frog,  indirect  excitation  witli  induction  currents  of  increasing  strength  at 
uniform  frequency  (10-12  per  sec.)    (Griitzner.) 

tively  high  coil  frequency.  With  the  constant  current,  too,  it 
may  often  be  observed  that  with  repeated  closure  at  fairly  short 
intervals,  a  current  ineffective  in  itself  will  gradually  produce 
effectual  excitation  (Engelmann),  This  property  of  summation 
of  stimuli  characterises  all  irritable  protoplasm  (ciliated  cells, 
nerve  cells,  vegetable  protoplasm,  e.g.  Dioncea,  etc.)  in  a  more  or 


120 


ELECTRO-PHYSIOLOGY 


less  modified  degree,  so  that  the  phenomena  described  in  muscle 
are  only  a  special  case  of  a  universal  principle.  Viewed  in  the 
light  of  the  relations  which  we  have  been  urging  between  an 
increase  of  excitability  produced  by  excitation,  and  the  process  of 
excitation  itself,  it  is  a  matter  of  indifference  whether  the  process 
be  regarded  as  a  true  "  summation "  of  ineffective  into  effective 
stimuli,  or  as  increase  of  excitability  produced  by  this  summation. 
The  following  points  with  regard  to  form,  process,  and  magni- 
tude of  tetanus  contraction,  and  its  dependence  upon  different 
variable  factors,  have  been  established  by  careful  researches  on 
the  striated  muscles  of  vertebrates  and  invertebrates.  When 
the  stimuli  are  weak,  and  the  frequency  per  sec.  moderate  (10— 
12),  the  curve  obtained  from  frog's  muscles  resembles  Fig.  51. 


Fig.  54.— Tetanus  arising  from,  and  resolving  into,  single  twitches.  The  beginning  and  end  of 
the  tracing  only  are  represented.  In  the  omitted,  central  portion  of  1"9  sec.  the  line  traced 
by  the  muscle  was  horizontal.    (Engelmann.) 


This  will  be  recognised  as  very  incomplete  tetanus,  with 
deep  indentations,  so  that  only  in  a  minor  degree  can  the  muscle 
be  said  to  be  permanently  shortened.  The  summits  of  the  in- 
dentations lie  almost  horizontal.  If  the  exciting  induction 
currents  are  strengthened,  or  increased  in  frequency,  the  teeth 
become  shorter  and  flatter,  and  the  indentations  less  deep ;  the 
muscle  reaches  a  much  higher  degree  of  permanent  contraction 
(Fig.  52).  Finally,  the  curve  rises  steeply  from  the  beginning, 
and  the  indentation  becomes  negligible,  disappearing  altogether 
in  complete  tetanus  (Figs.  53,  54).  According  to  Kohnstamm  (9) 
the  tetanus  becomes  more  incomplete  with  uniform  frequency,  in 
proportion  with  increasing  strength  of  stimulus,  since  every  incre- 
ment of  stimulation  accelerates  the  relaxation  of  the  single  con- 
traction (Fig.  54). 

Bohr  (7)  finds  that  the  tetanus  curve  of  unfatigued  muscle 
(frog,  toad)  is  "  an  equilateral  hyperbola  brought  to  an  asymp- 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  121 

tote,"  which  is  the  more  remarkable  since  the  increment  of 
single  twitches  in  the  "staircase,"  as  well  as  with  increasing  strength 
of  stimuli,  follows  the  same  law ;  yet  the  rule  can  hardly  be 
universal,  e.g.  the  tetanus  curve  of  hydrophilus  muscle  does 
not  coincide  with  it  (Eollett,  8).  The  difference  of  contraction 
magnitude  is  at  once  apparent  on  comparing  the  two  cases  of 
complete  tetanus  resulting  from  a  series  of  maximal  induction 
shocks,  and  a  single  contraction.  The  freely  contracting,  loaded 
muscle  invariably  shortens  more  in  tetanus  than  in  a  single  twitch. 
Even  if  it  were  certain  that  the  greater  height  of  tetanus  may  be 
explained  by  the  superposition  (as  described)  of  single  twitches, 
the  subsequent  course  of  the  process  remains  in  obscurity.  We 
can  only  conclude  from  the  fact  that  the  muscle  in  tetanus 
does  not  exceed  a  certain  maximal  shortening,  that  Helmholtz's 
law  loses  more  and  more  of  its  significance  with  progressive 
superposition,  each  new  stimulus  being  so  much  the  less  effective 
in  proportion  as  the  muscle  has  already  shortened  with  the  pre- 
ceding stimuli.  The  height  of  the  tetanus  curve  grows  with  the 
strength  of  excitation,  or,  where  this  is  constant,  with  its  frequency. 
The  steepness  of  the  rise  alters  in  the  same  proportions  (Ivohn- 
stamm,  9). 

A  fact  of  great  importance  in  the  estimation  of  tetanus  was 
determined  by  v.  Kries  and  v.  Frey  (10),  who  showed  that  arti- 
ficial support  of  the  muscle  would,  under  some  conditions,  pro- 
duce the  same  degree  of  contraction  from  a  single  stimulus,  as  in 
complete  tetanus.  In  this,  experiment  an  adjusting  screw  is 
placed  under  the  muscle-lever,  and  so  arranged  as  to  raise  it 
to  any  given  height.  The  loading  first  takes  effect  fully  upon 
the  muscle,  when  it  begins  to  raise  the  lever  from  the  support. 
The  fact  that  the  supported  muscle  contracts  as  vigorously  in  a 
single  twitch,  as  the  unsupported  muscle  in  the  more  pronounced 
tetanus,  is  very  apparent  when  single  twitches  and  tetani  are 
alternated  in  the  same  experiment.  If  the  muscle  is  sufficiently 
loaded,  the  tetanus  curve  rises  more  or  less  above  the  summits  of 
the  single  twitches  of  the  unsupported  muscle.  If  the  tetanus 
is  followed  by  a  row  of  "propped"  twitches  (Fig.  55,  o)  the 
parallelism  of  the  two  processes  is  very  apparent,  and  the  con- 
viction is  forced  upon  us  that  in  summation  of  twitches  in  muscle 
there  must  be  some  kind  of  under-propping  in  the  muscle ;  the 
effect  is,  as  G-rlitzner  (11)  says,  "  as  though  the  muscle  contracted 


122 


ELECTRO-PHYSIOLOGY 


SO  effectually  in  tetanus,  because  in  some  measure  it  forms  its  own 
support,  and  carries  itself"  (Fig  55). 

In  detail,  we  find  many  variations  with  regard  to  alteration 


Fig.  55.— a,  Gastrocnemius  (Frog);  single  twitches,  tetanus,  and  group  of  supported  twitclies, 
loaded  at  10'5  gr. ;  b,  tlie  same  at  0-5  gr.  loading,    (v.  Frey.) 

of  height  in  a  series  of  supported  twitches.  The  highest  summit 
of  the  curve  either  coincides  with  the  highest  adjustment  of  the 
supporting  screw  (as  in  the  above  example),  or  it  may  be  reached 

earlier,  in  which  case  the 
height  of  the  twitches  sinks 
again  with  further  increased 
propping.  Finally,  there  is 
the  case  in  which  height  of 
twitch  at  first  increases  with 
regular  progressive  support, 
then  decreases  and  finally 
rises  again  to  the  highest 
increment,  so  that  the  func- 
tion has  two  maxima  (v. 
Frey,  10-12)  (Fig.  56). 

These  relations  also  are 
expressed  in  certain  forms 
of  tetanus  curves  with  two  and  three  summits. 

All  these  facts  relate  to  the   proportionately  loaded  muscle. 
With   very    Hght    loading,   on   the   other    hand,   the    supporting 


Fig.  56. — Curarised  muscle  ;  series  of  twitches  with 
varying  support ;  load,  6  grs. ;  stimulation  inter- 
val, 1  sec.     (v.  Frey.) 


II  ■'    CHAXGE  OF  FORM  IN  MUSCLE  DURIXG  ACTIAITY  123 

has  little  effect  upon  the  position  of  the  summit  of  the  twitch, 
and  in  correspondence  with  this  the  difference  between  height 
of  tetanus  and  height  of  twitch  vanishes  (Fig.  55,  b).  This 
is  intelligible  when  it  is  remembered  that  at  low  tension  the  ex- 
ternal  conditions  of  the  process  of  contraction  cannot  be  intrinsic- 
ally altered  bj  the  support.  Tetani  lower  than  the  single  twitch 
are  frequent  in  fatigued  muscle  (Fig.  57).  When  a  muscle  has 
had  a  short  rest  after  a  prolonged  series  of  contractions,  the  first 
twitch  on  the  renewal  of  excitation  is  abnormally  high  in 
proportion  with  the  following  (Buckmaster's  "  initial "  twitch), 
and  this  reversal  of  relation  continues  even  if  the  muscle  is 
supported. 

At  present  there  are  insuperable  difficulties  in  the  w^ay  of  any 
adequate  explanation  of  all  these  relations,  and,  in  particular,  of 


Fio.  57.— Tetanus  and  single  twitch  of  a  fatigued  and  curarised  muscle  ;  load,  10  grs.;  rate  of 
stimuli,  0"1  see.     (v.  Frey.) 

exact  analysis  of  the  process  of  tetanus,  as  is  readily  understood 
when  we  consider  the  number  of  different  factors  in  the  tetanus 
curve.  The  staircase  appearance,  svperiwsition  in  Helmholtz's  sense, 
the  effect  of  internal  sv/piwrting,  as  well  as  fatigue  and  contracture, 
all  take  more  or  less  share  in  the  process  of  tetanus  (v.  Frey). 

Another  and  probably  important  factor  is,  that  in  the  majority  of 
cases  a  muscle  is  not  a  physiological  unit,  but  represents  a  mixture 
of  at  least  two  functionally  different  elements,  which  can  hardly 
be  supposed  to  act  simultaneously  and  uniformly.  This  leads 
to  the  further  question  of  the  dependence  of  tetanic  excitation 
upon  the  nature  of  the  muscle.  Here,  in  the  first  place,  we  must 
consider  the  widely  varying  duration  of  contraction  in  different 
muscles,  or  the  different  fibres  of  the  same  muscle.  An  uninter- 
rupted tetanus,  where  the  twitches  are  superposed  as  above,  can 
of  course   be  expected   only  when  the  interval  of  stimulation  is 


124  ELECTRO-PHYSIOLOGY  chap. 

equal  to,  or  smaller  than,  the  duration  of  twitch  up  to  the 
moment  of  maximal  shortening.  It  follows  immediately  from 
this,  that  to  yield  a  complete  tetanus  the  single  stimuli  must 
succeed  each  other  the  more  rapidly  in  proportion  with  the 
shortness  of  the  twitches.  In  the  case  of  a  twitch  as  rapid  as 
that  of  the  wing-muscles  of  certain  insects,  which  lasts  hardly 
•3^  sec,  more  than  300  stimuli  per  sec.  would  he  required  to 
produce  a  tetanus.  When  in  other  cases  the  contraction,  as  in 
the  muscles  of  the  tortoise,  lasts  ahout  1  sec,  two  stimuli 
per  sec.  will  produce  complete  tetanus.  This  is  most  striking 
in  the  smooth  muscles,  which  are  so  sluggish  that  it  is  conceivable 
that  an  incomplete  tetanus  may  be  produced,  even  when  the 
single  stimuli  (repeated  closure  of  a  constant  current  of  adequate 
strength)  are  separated  by  pauses  of  several  seconds. 

The  following  numbers  give  an  approximate  idea  of  the 
stimulation  frequency  per  sec.  required  to  produce  tetanic  fusion 
of  twitches  : — 


Tortoise 

Frog,  Hyoglossus  (slow) 

„     Gastrocnem.  (quick)   . 
Crab,  Claw-muscle  (slow)     . 

,,    .Tail-muscle  (quick)    , 
New-born  animal  (warm-blooded) 
Rabbit  (red  muscle) 

„       (pale) 
Bird 
Insects 


2  (Marey) 
10  to  15 
30 

20  (Richet) 
40 

16  (Soltmann) 
4  to  10  (Kronecker  and 
Stirling) 
20  to  30 
100  (Richet) 
300  to  400  (Marey,  Landois) 


It  is  obvious  that  the  above  figures  would  vary  considerably 
if  the  state  of  the  muscles  were  to  alter.  We  have  already 
emphasised  the  difference  in  duration  of  twitch  according  as  the 
muscle  at  the  time  of  experiment  is  fresh  or  fatigued,  with 
circulating  blood  or  bloodless,  is  normal  or  poisoned  (veratrin), 
warmed  or  cooled,  so  that  without  changing  the  frequency  of 
stimulation  we  may  have,  according  to  the  physiological  state  of 
the  muscle,  complete  or  incomplete  tetanus,  or  only  simple 
twitches.  Moreover,  a  glance  at  the  table  given  above  shows  what 
a  significant  difference  exists  in  the  stimulation  -  frequency 
required  to  tetanise  functionally  different  striated  muscles  in  the 
same  animal.  As  these  relations  are  of  great  importance,  they 
must    be    examined    more  in   detail.      Eanvier   (13)   first   drew 


II  ■    CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  125 

attention  to  the  remarkable  physiological  diflf'erences  between  red 
and  pale  muscles  in  the  raljbit,  and  more  particularly  to  the 
enormous  differences  which  he  found  in  the  stimulation-frequency 
required  to  produce  tetanus,  while  Kronecker  and  Stirling  (14) 
subsequently  ascertained  that  the  red  muscle  of  rabbit,  in  corre- 
spondence with  the  sluggish  process  of  contraction,  is  thrown  by 
4  stimuli  per  sec.  into  incomplete,  by  10  per  sec.  into 
fairly  complete,  tetanus.  With  stimulation  intervals  of  ^  sec. 
the  pale  muscle  recovers  its  extension  again  almost  completely, 
while  the  red,  though  trembling,  remains  tensely  contracted. 
The  pale  muscle  of  rabbit  requires  from  20  to  30  stimuli  for 
complete  tetanus.      Analogous   curves   are   obtained    from   corre- 


FiG.  58. — Tetanus  curve  of  tail-  and  claw-inuscles  of  Crab  with  uniform  excitation.  The  quick 
tail-muscles  fall  into  incomplete  clonic  tetanus,  the  sluggish  claw-muscles  into  complete 
tetanus.    (Richet.) 

spending  excitation  of  the  quick  tail-  and  sluggish  claw-muscles 
of  the  crab  (Pdchet,  4)  (Fig.  58). 

Very  characteristic,  and  functionally  weighty,  differences  of 
tetanus  contraction  were  found  by  Eollett  (8)  in  the  anatomically 
and  physiologically  different  muscles  of  hydrophilus  and  dytiscus. 
Besides  the  fact  that  in  this  case  also  the  quick,  rapidly-contract- 
ing muscles  of  dytiscus  require  a  higher  stimulation-frequency  to 
enable  them  to  contract  than  the  sluggish  muscles  of  hydro- 
philus, as  at  once  appears  from  Fig.  59,  a,  h,  another  important 
difference  exists  in  the  course  of  a  prolonged  and  complete 
tetanus.  The  first  tetani  yielded  by  freshly-prepared  dytiscus 
muscles  rose  more  steeply,  and  fell  much  more  rapidly,  than 
those    of   hydrophilus  muscles,  in  which    the    long   duration   of 


126 


ELECTRO-PHYSIOLOGY 


the  tetanus  is  highly  significant.  This  is  expressed  in  the  fact 
that  the  height  of  the  tetanus  alters  little  with  repeated  excita- 
tion in  hydrophilus,  while  in  dytiscus  it  rapidly  decreases. 
"  Hydrophilus  muscle,  notwithstanding  its  excitation,  remains 
capable  of  functioning  for  so  long  that  it  only  becomes  exhausted 
very  gradually,  provided  it  is  given  a  short  rest  between  the  pro- 


Ji 


V" 


ff 


Fig.  59. — Tetani,  a,  of  Dytiscus  ;  b,  of  Hydrophilus  muscle  at  uniform  excitation.    (Rollett.) 


longed  periods  of  activity  in  regular  order  of  succession.  Dytiscus 
muscle,  on  the  contrary,  is  exhausted  by  exertion  in  a  compara- 
tively short  time,  but  if  it  is  given  longer  rest  between  the 
periods  of  exhaustive  activity,  it  can,  in  spite  of  repeated  efforts, 
recover  itself  between  times  to  a  certain  extent  in  the  intervals." 
Dissimilation  and  assimilation  must  accordingly  take  a  different 
course  in  the  two  kinds  of  muscle.      Eichet  (I.e.  p.   114)  made 


II  CHAJv'GE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  127 

similar  observations  in  regard  to  the  process  of  tetanus  with 
prolonged  excitation,  in  the  sluggish  elaw-  and  quick  tail-muscle 
of  the  crab.  Complete  tetanus  of  the  latter  is  never  of  long 
duration,  the  muscle  quickly  relaxes,  and  for  some  time  exhibits 
a  marked  diminution  of  excitability ;  the  tetanus  of  the  claw- 
muscles,  on  the  other  hand,  increases  gi^adually,  and  may  persist 
for  a  long  time.  The  relation  of  this  phenomenon  to  the  normal 
activity  of  both  kinds  of  muscle  is  unmistakable.  The  powerfully 
developed  adductor  of  the  claw  has  to  remain  uniformly  con- 
tracted for  a  long  period  with  a  great  output  of  energy,  while 
the  tail  serves  up  quick  movements  (strokes)  like  a  rudder,  and  is 
concerned  less  with  a  prolonged  yield  of  energy  than  with  rapidity 
of  motion. 

These  results  are  an  additional  confirmation  of  the  conclusions 
which  we  have  shown  to  stand  out  re  energy  and  duration,  from 
the  distribution  and  presence  of  sarcoplasmic  and  non- sarcoplasmic 
(light  and  dark,  i.e.  pale  and  red)  muscles.  The  same  facts  assume 
a  still  greater  importance  when  it  is  remembered  that  in  the 
majority  of  cases  one  muscle  contains  hoth  Jdnds  of  functionally 
different  fibres  in  varying  quantitative  relations.  And  if  this 
double  composition  appears  sometimes  in  a  single,  simple  twitch, 
and  is  plainly  expressed  in  the  curve,  the  same  also  occurs, 
and  in  a  much  more  marked  degree,  in  tetanus.  Generally 
speaking,  we  may  expect  that  muscles,  the  bulk  of  which  consists 
chiefly  of  sluggish  (dark,  red)  fibres,  will  exhibit  properties  in 
conformity  with  these,  while,  if  composed  of  quick  fibres,  they 
will  react  like  the  latter. 

This  is  well  indicated,  according  to  Grlltzuer  (15),  in  the 
relation  between  the  height  of  the  single  twitches  and  the  height 
of  tetanus.  In  loaded  muscle  the  latter  considerably  out-tops  the 
former ;  but  under  uniform  conditions  the  difference  is  much 
more  marked  in  sluggish  than  in  quick  fibres.  If,  e.g.,  with  direct 
excitation,  the  height  of  tetanus  in  the  mixed  gastrocnemius  in 
frog  and  toad  are  compared,  it  will  be  seen  that  the  muscle 
of  the  latter,  which  mainly  consists  of  sluggish  fibres,  will  raise 
the  same  weight  much  higher  than  the  corresponding  muscle 
of  the  frog,  although  it  is  much  smaller.  The  former  almost 
curls  itself  into  a  ball  with  strong  electrical  stimulation,  while  the 
frog's  muscle,  even  in  the  most  pronounced  tetanus,  is  far  from 
being  rolled    up.       While  in  the  "  quick "  muscles  of    the  frog 


128  ELECTRO-PHYSIOLOGY 


(triceps,  gastrocnemius)  the  height  of  twitch  to  that  of  tetanus  is  as 
1  :  2—3,  the  ratio  in  the  same  muscle  of  the  toad  is  about  1  :  5, 
and  it  is  considerably  larger  in  the  more  sluggish  muscles  (hyo- 
glossus  and  rectus  of  frog,  1  :  8—9).  In  investigating  isometric 
muscular  action  in  man  (M,  obductor  indicis  or  interosseus  dorsalis 
primus)  by  a  specially  constructed  tension  indicator,  Fick  (16) 
found,  on  comparing  the  tension  produced  by  a  maximal  single 
stimulus  with  that  developed  by  tetanising  excitation,  that  the 
latter  is  ten  times  as  great  as  the  former,  while  in  the  frog  the 
difi'erence  is  much  less,  whether  in  isotonic  or  isometric  action. 
Human  skeletal  muscle  therefore  reacts  in  complete  correspondence 
with  red  sluggish  fibres. 

Bearing  in  mind  these  results,  which  show  that  the  work 
yielded  in  tetanus  by  the  quick  (pale,  clear)  muscles  is  insignificant 
both  as  regards  size  of  weight  lifted  and  height  to  which  the 
load  is  raised,  in  comparison  with  the  same  yield  of  the  sluggish 
(dark,  red)  muscles,  we  may  adopt  Griitzner's  denotation  of  the 
latter  as  "  tetanus  muscles,"  since  they  may  be  said,  through 
their  physiological  properties,  to  be  adapted  to  this  form  of  shorten- 
ing, and  singularly  fecund  in  their  response.  When  quick  and 
sluggish  fibres  are  united  in  the  same  muscle,  it  may  result  from 
the  differences  of  excitability  as  above,  that  with  weak  excitation 
(direct,  or  from  the  nerve)  different  portions  of  the  muscle  twitch, 
or  go  into  tetanus,  from  those  brought  into  play  with  stronger 
excitation.  Grriitzner  is  even  inclined  to  ascribe  the  summation- 
effect  in  tetanus  in  great  part  to  these  differences  in  the  physio- 
logical response  of  the  two  kinds  of  fibres.  He  refers  (11,  p.  250) 
the  striking  similarity  between  a  series  of  "  supported  "  twitches, 
and  tetanus  {supra),  to  an  internal  supporting  of  the  muscle  by 
its  sluggish  (dark,  red)  fibres.  These  keep  it  at  rest  at  a  given 
medium  length,  which  naturally  decreases  inversely  to  the  number 
of  red  fibres.  If  an  appropriate  stimulus,  i.e.  not  too  powerful, 
is  sent  into  the  muscle  when  thus  shortened,  its  excitable  (light) 
portions  will  contract  visibly.  This  second  superposed  contraction 
must  accordingly  result  more  quickly,  as  v.  Kries  found  actually 
was  the  case  (shortening  of  apex  -  time).  The  stronger  the 
stimulus,  however,  the  greater  will  be  the  activity  of  the  more 
sluggish  portions ;  the  more  rapidly  will  the  discontinuity  vanish 
(which,  as  might  be  expected,  is  disputed  by  Kohnstamm),  and 
the  Greater  will  be  the  height  of  the  "  tetanus  curve." 


II  CHANGE  OF  FORM  IN  MUSCLE  DURIN(;  ACTIVrrV  129 

"  This. then  affords  a  simple  explanation  of  the  fact,  which  is 
easy  to  confirm,  that  twitches  may  be  elicited  from  a  muscle  that 
is  already  in  steady  and  uniform  contraction,  as  follows  indeed 
in  a  great  number  of  cases  "  (Griitzner). 

Upon  this  assumption,  which,  as  it  seems  to  us,  emphasises 
one  of  the  most  essential  and  important  factors  that  comes  into 
play  in  tetanus  contractions,  "  a  tetanus  remains  discontinuous 
and  unstable  as  long  as  the  twitches  of  the  pale  fibres  can  be 
superposed  upon  the  contraction  of  the  red.  But  if  the  red  have 
shortened  to  their  maximum,  the  entire  muscle  will  be  so  short 
that  the  twitching  movements  of  the  pale  muscles  produce  little 
or  no  discontinuity  of  movement,  or  tremor." 

On  account  both  of  its  histological  and  physiological  pro- 
perties, cardiac  muscle  naturally  falls  under  the  same  category  as 
the  sluggish,  sarcoplasmic,  striated  skeletal  muscles.  In  corre- 
spondence with  its  sluggish  twitch  and  prolonged  duration,  we 
might  naturally  expect  to  find  it  peculiarly  adapted  to  steady, 
complete  tetanus.  Yet  the  contrary  results  from  experiment,  and 
in  this  respect,  as  in  many  others,  cardiac  muscle  takes  up  a  char- 
acteristic attitude.  Summation  experiments  are  the  more  readily 
carried  out  on  the  heart,  since  its  spontaneous  rhythmical  con- 
tractions, which  are  undoubtedly  valid  in  a  physiological  sense 
as  single  twitches,  may  be  employed  in  a  slow  series  of  beats 
(frog's  heart)  to  investigate  the  action  of  a  new  artificial  stimulus 
(induction  shock)  in  different  phases  of  contraction  and  relaxation. 
In  these  experiments  Marey  (17)  found  that  cardiac  muscle  in 
certain  phases  of  its  activity  was  variably  sensitive  to  excitation 
by  a  single  induction  shock,  while  during  one  period  it  is  not  at  all 
excitable  (refractory).  The  ventricle,  and  all  other  sections  of  the 
heart,  are  unresponsive  to  moderate  stimuli  during  the  entire 
systole  of  the  parts  in  question,  wdiile  in  the  diastolic  period,  as 
well  as  in  the  pause  between  each  stimulus,  an  extra  contraction  is 
yielded.  With  stronger  excitation  this  "  refractory  period "  is 
more  and  more  abbreviated,  and  very,  strong  stimuli  seem  finally 
to  produce  an  excitatory  effect  in  every  sphere  of  cardiac  activity 
(Marey,  Tigerstedt,  Loven,  etc.).  This  remarkable  property  of 
all  cardiac  muscle  will  partially  explain  the  characteristic  reaction 
of  the  heart  during  a  rapid  succession  of  (tetanising)  stimuli ; 
for  it  is  evident  that  in  consequence  of  this  peculiarity  a  con- 
stant, or  raj^idly  repeated,  excitation  must  fail   to   produce   any 

K 


130 


ELECTRO-PHYSIOLOGY 


continuous,  or  sunnnated,  contraction  (tetanus) ;  there  can  only 
be  a  series  of  contractions  interrupted  by  marked  pauses.  Bow- 
ditch  was  the  first  to  determine  by  excitation  of  the  frog's  heart 
that  even  where  the  single  induction  shocks  are  separated  by 
intervals  of  several  seconds,  the  number  of  the  contractions  is 
often  less  than  that  of  the  stimuli.  This  disproportion  betw^een 
stimulus  and  contraction  is  even  more  striking  where  the  former 
are  working  in  quick  succession,  when  the  muscle  of  the  heart  will 
often  fail  to  respond  to  a  whole  series  of  excitations  (Basch,  5). 
Under  these  conditions  a  new  cardiac  rhythm,  dependent  on  in- 


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Fig.  60.  —  Bulbus  aorte  (Frog),  tetanisiiig  excitation  with  induction  currents.  Stimulation- 
frequency,  80  per  sec.  Tuning-fork  tracing,  ^  sec.  The  ciphers  under  the  figures  give  in- 
tensities of  tetanising  currents.    Intensity  of  coil  pushed  home= 1000.    (Engelniann.) 


tensity  and  frequency  of  the  stimulus,  is  always  developed,  since,  as 
Engelmann  (6)  found  on  tetanising  the  bulb  of  the  frog's  heart 
with  alternating  currents,  a  very  low  excitation-strength  will, 
after  some  time,  produce  a  sj'stole  by  "  latent  summation," 
followed  perhaps  by  another,  or  several.  The  latent  period  of 
the  first,  and  the  intervals  of  the  subsequent,  contractions,  are 
longer  in  proportion  as  the  single  stimuli  are  weaker.  AVith 
growing  density  of  the  exciting  current  the  duration  of  the 
latent  period  soon  becomes  minimal,  as  also  the  interval  between 
each  systole  (Fig.  60).  Even  with  the  strongest  currents 
Engelmann  found  no  complete  relaxation  of  the  bulb  after  tlie 
first   contraction ;    it    remained    in    tetanus   at  a   ceitain   height. 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  1:31 

Yet  we  have  here  no  true  superposition  of  contractions,  but  the 
first  lift  is  of  the  same  height  as  after  a  single  effective  stimulus. 
At  first,  interruptions  may  still  be  seen  in  the  tetanus  curve,  the 
period  of  which  is  not,  however,  that  of  the  stimulus,  but  longer, 
intrinsic  to  itself,  and  determined  by  the  specific  nature  of  the 
muscle- substance.  Eanvier  (18)  obtained  the  same  tetanus 
curves  from  the  ventricle  of  the  frog's  heart.  It  cannot  be 
doubted  that  this  reaction  of  the  cardiac  bulbar  muscles  to 
tetanising  excitation  stands  in  the  closest  relation  with  their 
highly-developed  faculty  of  rhythmical  activity  ;  we  know  that 
perfectly  constant  stimuli,  e.g.  chemical  and  mechanical,  produce 
rhythmical  contractions  of  cardiac,  and  also  under  certain  condi- 
tions of  striated  skeletal,  muscle  during  the  entire  duration  of 
their  action ;  this  property  is,  however,  much  less  developed  in 
the  latter  than  in  the  former. 

We  must  assume  that  a  series  of  single  stimuli  would 
approximate  the  more  closely  in  their  physiological  effect  to  the 
action  of  a  persistent  stimulus,  in  proportion  with  the  rapidity  of 
succession  of  the  stimuli,  so  that  it  would  not  be  surprising  if, 
under  certain  conditions,  the  effect  of  a  succession  of  stimuli 
corresponded  with  that  of  a  persistent  stimulus  in  striated  skeletal, 
as  in  cardiac,  muscle.  This  does,  indeed,  appear  to  be  the  case, 
and  two  phenomena  especially  are  remarkable  as  claiming  atten- 
tion in  this  particular,  i.e.,  on  the  one  hand,  the  rhythmically 
interrupted  tetanus,  on  the  other,  the  so-called  initial  contraction. 
Eichet  (4,  p.  126)  was  the  first  to  describe  rhythmical  alterations 
in  the  curve  of  tetanised  crab's  claw-muscle,  for  which  it  appears 
that  weak  and  very  frequent  stimuli  are  essential.  Schoenlein 
(19)  (Fig.  61,  a,  h)  soon  after  made  similar  observations  on 
beetle  muscles  (dytiscus  and  hydrophilus).  He  obtained,  on 
exciting  the  muscles  in  the  detached  femur  with  induction 
currents  of  low  strength  and  high  frequency,  either  rhythmical 
contractions  (dytiscus),  or  rhythmically  interrupted  tetani  of 
longer  duration  (hydrophilus,  crab),  or  finally  contractions,  separ- 
ated by  pauses  of  rest  at  different  intervals.  The  stimulation- 
frequency  in  these  experiments  was  usually  880  per  sec,  but  the 
phenomena  may  be  observed  at  much  higher  frequencies.  The 
lower  threshold  is  in  the  beetle  100  or  80,  in  crab  as  low  as  30 
per  sec. 

As    regards    current    strength,    the  rhythm  varied  between 


132 


ELECTRO-PHYSIOLOGY 


CHAP. 


minimal  stimulation  distance  and  1-2  mm.,  a  very  small 
interval  of  difference.  With  closer  approximation  the  rhythm 
always  passed  into  a  smooth,  unbroken  tetanus.  Here,  again, 
the  difference  already  pointed  out  between  the  muscles  of 
hydrophilus  and  dytiscus  is  apparent,  since,  as  we  have  seen,  the 
former,  like  the  sluggish  claw-muscles  of  the  crab,  yield  longer, 
rhythmically  interrupted  tetani,  while  the  frequent  rhythmical  con- 
tractions characteristic  of  dytiscus  under  tlie  same  conditions  are 
nowhere  present.      We  have  no  hesitation  in  claiming  for  these 


Fig.  61. — a,  Rliythinical  contractions  of  leg  of  Dytiscus  niarginalis  with  tetanising  excitation. 
Stimulation  -  frequency,  880  per  see.  b,  Rhythmically  interrupted  tetani  from  leg  of 
Hydrophilus  piceus.     (Schoenlein.) 

observations  of  Schoenlein  and  Eichet  an  analogy  with  the  fact 
that  cardiac  muscle  also  yields  rhythmical  contractions  under  the 
same  conditions,  although,  of  course,  we  have  in  these  to  reckon  be- 
sides with  the  value  of  the  single  twitches,  which  is  never  or  rarely 
the  case  in  beetle  muscle.  In  the  quick  muscles  of  dytiscus,  in 
which  the  frequency  of  rhythmical  contraction  varies  at  an 
average  of  2—6  per  sec,  exceptionally  rising  to  30,  it  is  perhaps 
legitimate  to  credit  the  single  contractions  with  the  value  of 
single  twitches,  while  the  sluggish  hydrophilus  and  crab  muscle 
throughout  exhibit  short  tetani.  We  shall  presently  see  that 
cardiac    muscle    always,  and   striated   skeletal   muscle    under  at 


CHAXGE  OF  FORM  IN  MUSCLE  DUFJX(i  ACTIVITY  133 


least  sorii6  circiiinstances,  are  stimulated  by  the  constant  current 
to  quite  analogous  rhythmical  activity.  As  a  rule,  however,  the 
constant  current  only  produces  a  single  contraction  when  it  is 
closed,  and  eventually  when  it  is  opened  also  (make  and  break 
twitch),  in  striated  muscle,  both  with  direct  or  indirect  (vid  nerve) 
excitation.  Interrupted  currents  have  exactly  the  same  effect 
under  certain  conditions. 

Bernstein  (20)  was  the  first  to  observe  tliat  with  a  given 
frequency  (about  900  per  sec),  and  moderate  intensity,  induction 
currents  led  into  the  frog's  sciatic  produced  a  single  brief 
"twitch"  of  the  gastrocnemius,  a  so-called  "initial  twitch," 
instead  of  tetanus ;  this  is  more  apparent  in  the  most  rapid 
interruptions  of  the  primary  circuit,  growls  Aveaker  with  diminish- 
ing frequency  of  stimulation,  and  disappears  entirely  below  a 
certain  limit  (200  to  300  stimuli  per  sec.)  The  phenomenon 
occurs  with  both  direct  and  indirect  excitation  of  curarised 
muscle.  According  to  Grunhagen  (21)  and  Engelmann  (22) 
there  is  occasionally  a  "  final  twitch  "  at  the  close  of  the  tetanus 
also,  corresponding  with  the  opening  twitch  of  the  constant 
current.  The  investigation  of  the  effects  of  very  high  stimula- 
tion-frequencies on  muscle  (and  nerve)  often  leads  to  contra- 
dictory results,  because  the  application  of  electrical  stimuli  of 
great  rapidity  presents  great  technical  difficulties,  where  complete 
uniformity  in  strength  and  order  of  succession  is  required. 
Neither  the  application  of  sliding  contacts,  nor  mercury  closure, 
is  in  this  respect  sufficiently  trustworthy.  Even  Kronecker's 
"acoustic  current  interrupter"  (14),  in  wdiich  the  longitudinal 
vibrations  of  a  magnetised  iron  rod,  produced  hj  friction,  set  up 
induction  currents  in  a  ware  coil,  fails,  according  to  Eoth  (23), 
at  very  high  frequencies  (over  4000  vibrations).  Eoth  (I.e.)  has 
recently  employed  the  microplione,  and  obtained  reliable  electrical 
stimuli  of  high  frequency,  which  were  also  regular  and  perfectly 
under  control.  Pipes  of  different  pitch  were  blown  1)y  means  of 
a  gas  motor,  and  a  dry  cell,  equal  to  one  Leclaiiche,  was  intro- 
duced into  the  primary  circuit.  With  indirect  excitation  of  a 
frog's  gastrocnemius  (from  the  nerve)  Eoth  found  that  tetanus 
disappeared  when  5000  stimuli  per  sec.  were  sent  in  from  a  pipe 
of  2500  vibrations,  with  a  given  strength  of  the  Blake  micro- 
phone. The  limit  with  direct  excitation  of  the  muscle  lay  under 
similar    conditions    about    300    stimuli   lower.       V.   Kries    sue- 


134  ELECTRO-PHYSIOLOGY  chap. 

ceecled  in  obtaining  oscillations  of  great  freqnency  by  the  use 
of  induction  coils,  produced  by  the  rotation  of  a  disc  between  the 
free  surface  of  the  iron  axis  of  a  coil,  and  the  opposite  pole  of  a 
powerful  electro-magnet,  the  periphery  of  the  disc  consisting 
alternately  of  iron  and  a  non-magnetic  substance  (brass).  Since 
each  iron  tooth  of  the  disc  is  magnetised  as  it  passes  o^-er,  a 
corresponding  change  occurs  in  the  magnetism  of  the  iron  axis  of 
the  coil,  and  current  is  induced.  The  frequency  of  current- 
oscillation  is  equal  to  the  number  of  iron  teeth  wdiich  run 
between  the  iron  core  and  the  pole  of  the  magnet  in  a  unit  of 
time.      (A  similar  apparatus  was  constructed  later  by  Griitzner.) 

Eoth,  as  well  as  y.  Kries,  showed  that  an  upper  limit  of  the 
stimulation-frequency  at  which   tetanus   can  still  be   called   out 
exists  only  relatively.      "  For  each  intensity  of  current  given  as 
the  amplitude  of  an  oscillatory  process,  a  frequency  may  be  deter- 
mined which  need  only  be  exceeded  in  order  to  produce  disappear- 
ance of  excitation  effects."     In   order,  tlierefore,  to  maintain  a 
tetanus,  intensity  as  well  as  frequency  must  be  augmented,  other- 
wise the  phenomenon  of  the  initial  twitch  will  ensue,  which  is 
described  by  Eoth  as  a  very  brief  tetanus,  while  Schoenlein  (25) 
regards  it  as  a  single  twitch  due  to  the  summation  of  ineffective 
stimuli.      V.  Kries  {I.e.)  also  finds  that  the  time-relations  of  the 
initial  twitch  correspond  throughout  with  simple  induced  twitches. 
If  the  frequency  in  a  given  case  remains  constant,  and  current 
intensity  only  diminishes,  the  effect  remains  approximately  con- 
stant (Kraft,  26).    An  appearance  analogous  to  the  "initial"  and 
"  final "   twitches  was  observed  by  Engelmann  (6),  during  very 
frequent   rhythmical   excitation,   in   the   smooth   muscle   of    the 
rabbit's  ureter,  where  "  the  close  of  a  series  of  periodically  recur- 
ring, short  stimuli  acts  like  the  break  of  a  constant  current,  just 
as  the  impact  of  a  rapid  succession  of  shocks  acts  like  the  closure 
of  a  constant  current."     We  haA'e  made  similar  observations  on 
the   adductor  muscle  of  Anodonta  (27).      And   an   effect  corre- 
sponding  with    the   initial    twitch  may   be   observed   in    cardiac 
muscle  :    "  If  a   succession   of  stimuli   (induction  shocks)   which 
would  produce  a  twitch  after  each  pause  of  two  or  more  seconds 
with  unfailing  regularity,  are  sent  into  the  excised  ventricle  at 
intervals  of  less  than  a  second,  the  first  stimulus  will  be  followed 
by   a   systole,    the   later   at   most    effect   a    weak   local   action " 
(Engelmann,  22). 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVIT^'  135 

Eeturning  to  the  consideration  of  steady,  complete  tetanus, 
we  have  next  to  ask  whether  the  excited  state  of  the  muscle  is 
really  continuous,  as  it  appears  from  the  curve  to  be,  or  if,  not- 
withstanding appearances,  discontinuous  alterations  of  condition 
can  be  demonstrated,  which  follow  in  the  usual  course,  but  are 
not  expressed  in  corresponding  form-changes.  It  is  concei^'able 
that  the  contractile  elements  of  the  muscle  may  be  thrown  into 
new  equilibrium,  and  maintained  at  the  same  as  long  as  excita- 
tion continues,  by  the  stimuli  which  follow  at  a  given  rapidity  ; 
or  we  may  assume  not  only  the  excitation,  but  also  muscular 
contraction  itself,  to  be  a  discontinuous  process,  in  which  a 
vibratory  movement  of  the  smallest  particles  of  the  muscle-fibres 
corresponds  with  each  impact  of  stimulation.  Experimentally, 
there  is  strong  reason  for  supposing  that  electrical  tetanus  is 
really  discontinuous,  notwithstanding  its  apparent  continuity.  If 
we  touch  a  muscle,  or,  better,  a  whole  limb,  that  is  in  rigid 
tetanus,  a  vibration  is  easily  felt  which  can  be  expressed  object- 
ively by  delicate  graphic  methods,  as  well  as  subjectively  in  the 
so-called  muscle-sound  or  muscle-tone,  and  by  the  tremor  of  the 
shiny  surface  of  the  muscle  in  tetanus,  as  Brticke  (28)  observed 
through  the  skin  of  a  man's  arm  when  suitably  illuminated. 
Helmholtz  obtained  an  objective  demonstration  of  the  vibrations 
of  tetanised  muscle  by  fixing  a  watch-spring  or  paper  flag  on  to 
an  elastic  board,  attached  to  the  muscle  (29).  The  springs 
vibrate  consonantly  when  their  own  vibration  period  coincides 
with  that  of  the  tetanised  muscle.  And  a  thread  attached  to  the 
tendon  of  such  a  muscle,  and  stretched  tensely,  falls,  as  Engel- 
mann  (22)  showed,  into  longitudinal  vibrations,  which  can  com- 
municate perceptible  impacts  to  a  light  recording  lever.  Since, 
further,  rapid  vibrations  {e.g.  of  tuning-forks)  may  be  conveyed 
through  air-capsules  with  perfect  accuracy,  the  quick  tremor  of 
the  tetanised  muscle  is  able,  without  an}^  noticeable  change  in  its 
length,  to  set  the  lever  vibrating  at  comparatively  large  ampli- 
tudes according  to  the  above  method,  cf  Marey's  inncc  myo- 
grapMque  (Kronecker  and  Hall,  3  ;  v.  Limbeck,  30). 

These  facts  are  even  more  interesting  in  reference  to  the 
much-disputed  question  whether  the  natural,  voluntary  or  reflex, 
persistent  contraction  of  striated  muscle  is  produced  by  a  rhyth- 
mically self-repeating  impulse,  as  in  artificial  tetanus. 

Wollaston  (1810)  and  Ermann   (1812)  attempted  to  apply 


136  ELECTRO-PHYSIOLOGY 


the  muscle- sound  in  determining  the  discontinuous  nature  of 
vohmtary  muscular  contraction  (Martins,  31),  and  Hehnholtz 
subsequently  investigated  the  phenomenon  more  exactly.  Like 
Ermann  he  started  from  the  fact  that  when  the  masticatory 
muscles  are  forcibly  contracted  at  night,  with  the  ears  closed,  "  a 
dull,  humming  sound  is  heard,  the  ground-tone  of  which  is  not 
intrinsically  altered  by  increased  tension,  while  the  humming  that 
goes  with  it  becomes  stronger  and  louder.  Helmholtz  then  found 
that  on  tetanising  his  ow^n  masseter  directly,  and  the  brachial 
muscles  of  an  assistant  from  the  median  nerve,  by  means  of 
an  induction  coil  standing  in  the  next  room,  the  muscle 
gave  the  tone  of  the  interrupting  sijring  instead  of  the  normal 
muscle-bruit.  This  is  a  direct  proof  that  vibrations  do  occur 
within  the  muscle,  however  constant  its  change  of  form  may 
appear  to  be,  and  that  a  vibration  actually  corresponds  with 
each  single  stimulus,  for  if  the  number  of  stimuli  is  altered, 
the  height  of  the  muscle-tone  alters  also,  since  within  certain 
limits  it  always  corresponds  with  the  stimulation-frequency.  That 
no  alteration  of  form  is  to  be  seen  in  the  tetanised  muscle  only 
implies  that  vibrations  occur  in  the  smallest  particles,  while  the 
external  shape  does  not  alter,  much  as  a  rod  that  is  vibrating 
longitudinally  emits  a  sound,  although  no  external  change  of  form 
is  visible.  Moreover,  as  pointed  out  by  Hermann,  the  muscle- 
sound  could  still  be  explained  if  the  periodic  process  in  tetanised 
muscle  were  not  merely  mechanical,  since  the  rhythmical  currents 
of  action  to  be  discussed  below  appear  to  be  sufficient  to  account 
for  them. 

The  experiments  of  Helmholtz  indicate  a  high  degree  of 
mobility  in  the  least  particles  of  striated  muscle,  for  he  even 
detected  a  clear  muscle-tone  of  corresponding  pitch  in  electrical 
tetanisation  of  240  stimuli  per  sec.  Bernstein  (33)  subse- 
quently endeavoured  to  determine  the  range  in  which  it  was 
possible  still  to  detect  a  clear  muscle-tone,  i.e.  to  what  limit  the 
muscle-elements  responded  to  the  rapidity  of  the  stimuli  acting 
on  them  in  electrical  tetanus.  By  means  of  the  acoustic  current- 
interrupter  (in  which  a  vibrating  spring  of  different  tensions  opens 
and  closes  the  primary  circuit)  he  stimulated  the  gastrocnemius 
muscles  of  the  rabbit,  partly  directly,  partly  from  the  nerve,  and 
convinced  himself  that  the  muscle-bruit  can  reach  a  very  consider- 
able height,  since  a  tone  of  748  vibrations  still  sounds  loudly, 


n  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  137 

and  one -of  93o  vibrations  is  faintly  audible.  At  a  frequency  of 
1056  stimuli,  however,  only  a  tone  a  fifth  or  an  octave  lower  was 
perceptible.  Loven  (34)  places  the  limit  of  reaction  in  rabbit 
muscle  much  lower.  When  all  due  precautions  were  taken,  he 
heard  from  M.  tibialis  anticus,  on  exciting  its  nerve  with  very 
weak  induction  currents  at  a  frequency  of  330—380  per  sec,  a 
tone  which  was  nearly  always  a  distinct  octave  below  the  tone  of 
the  interrupter ;  it  disappeared  on  intensifying  the  strength  of 
current,  and  reappeared  finally  at  a  certain  intensity  in  tmison 
with  the  exciting  tone.  In  individual  cases  the  two  octaves 
appeared  with  medium  stimulation,  sometimes  simultaneously, 
sometimes  alternating  with  one  another.  But  a  true  muscle-tone 
was  never  emitted  at .  a  higher  frequency  than  880  per  sec, 
corresponding  to  a",  which  the  muscle  responded  by  a\  the  lower 
octave.  With  higher  frequency  of  stimulation  a  dull,  muscular 
bruit  only  is  heard,  and  no  tone  corresponding  to  it.  Experiments 
in  which  the  sciatic  nerve  was  tetanised  by  the  telephone  gave 
similar  results.  With  progressive  alterations  of  pitch  by  singing 
into  it  the  scale  from  ^  (198  vibrations)  to  ^  (396  vibrations), 
Loven  clearly  heard  the  whole  scale  given  out  by  the  muscle  up 
to  c'  (264  vibrations);  the  d'  was  very  indistinct,  e',Jis',  and  ^, 
on  the  other  hand,  again  produced  clear,  muscular  tones,  but  they 
belonged  to  the  lower  octave.  Kronecker  and  Stirling  (14)  had 
found  that  on  stimulating  the  pale  gastrocnemius  of  rabbit  with  a 
Konig's  tuning-fork  (180  vibrations),  introduced  into  the  induction 
apparatus,  or  with  the  rapidly- vibrating  Wagner's  hammer,  the 
tone  corresponding  to  the  number  of  vibrations  in  the  interrupter 
was  heard  with  every  characteristic  of  its  pitch,  "  as  if  the  con- 
ducting wires  were  sound  conductors."  But  this  experiment  is 
not  confirmed  by  Loven.  In  every  case,  even  on  singing  into  the 
telephone,  "the  muscle -tone  was  conspicuously  dull  and  low- 
pitched,"  only  the  ground-tone  of  its  deeper  octave  being  given 
out,  never  the  over-tones.  Wedenski's  observations  (35),  which 
refer  specially  to  the  detection  of  the  action  currents  of  tetanised 
muscle  by  the  telephone  (infra),  also  indicate  that  the  capacity  of 
striated  muscle  to  respond  to  very  frequent  stimuli  by  correspond- 
ing, rhythmical  alterations  of  state,  is  limited.  Previous  to  the 
upper  limit  of  rhythmical  stimulation-frequency,  at  which  the  muscle 
only  replies  by  a  dull,  unmusical  sound,  an  exception  occurs  to  the 
rule  that  holds  at  the  beginning — i.e.  that  pitch  corresponds  w4th 


138  ELECTRO-PHYSIOLOGY 


stimulation-frequency,  since  the  tone  produced  is  an  octaYe,  a  fifth,  or 
eYen  two  octaYes  lower.  According  to  "Wedenski  there  is  complete 
parallehsm  between  the  electrical  oscillations  and  the  mechanical 
(audible)  ^dbrations  of  the  muscle,  in  the  sense  that  the  pitch  of 
both  tones  is  identical.  The  muscle  responds  to  each  Yery 
frequent  excitation  by  a  characteristic  bruit,  but  not  by  a  tone  of 
corresponding  pitch.  The  limit  in  warm-blooded  muscles  lies  at 
about  1000  stimuli  per  sec.  :  in  frog's  muscle  it  is  much  lower : 
according  to  Wedenski  this  last  ceases  to  give  a  tone  corresponding 
with  the  stimulation -frequency  at  about  200  stimuli  per  sec. 
LoYen  usually  failed  in  hearing  any  mechanical  tone  (caused  by 
Yibrations)  in  the  gastrocnemius  of  the  frog,  even  with  the  help  of 
the  most  sensitive  instruments.  This  seems  to  indicate  that  the 
capacity  of  muscle  to  produce  a  musical  tone  in  response  to 
rhythmical  excitation  is  the  more  developed  in  proportion  Y"ith 
the  mobility  of  the  muscle,  i.e.  with  the  rate  of  its  contraction. 
(Birds'  muscles  Y'ould  presumably  respond  to  very  high  frequencies: 
the  pale  muscle  of  mammals,  according  to  Ivronecker  and  Stirling, 
I.e.,  far  surpass  the  red  in  this  particular :  tortoise  muscle  emits 
hardly  any  sound,  or  only  at  a  comparati^'ely  low  frequency.)  It 
also  appears  that  the  capacity  of  a  muscle  to  giYe  out  sound 
suffers  considerable  Yariations  if  the  mobility  of  the  smallest 
particles  is  from  any  cause  diminished.  This  specially  applies 
to  fatigue,  to  which  is  owing  the  fact  that  a  muscle  which,  at  the 
beginning  of  excitation,  gives  out  a  tone  of  corresponding  pitch, 
subsecpiently  produces  a  deeper  sound,  and  eventually  only  an 
indefinite  murmur  (Wedenski,  I.e.)  Finally,  the  character  of  the 
muscle-tone  depends  also  upon  intensity  of  the  single  stimuli : 
where  tliis  is  Yery  low  an  undefined  murmur  replaces  the  musical 
tone  at  maximal  excitation,  in  spite  of  an  adequate  stimulation- 
frequency. 

The  fact  that  the  muscle-tone  does  not  always  correspond 
with  the  frequency  of  stimulation  in  direct  excitation  from  the 
nerve,  makes  conclusions  as  to  the  rhythm  of  central  innervation, 
deduced  from  the  natural  muscle-bruit,  very  uncertain.  We  have 
said  above  that  muscles,  when  thrown  voluntarily  into  vigorous 
and  persistent  contraction,  emit  a  dull,  humming  sound.  It  is 
difficult  to  determine  the  pitch  of  the  ground-tone  in  this  case, 
because  it  lies  on  the  threshold  of  perceptible  tones.  Helmholtz 
estimated    it    in    his    masticatorv  muscles  at    36  —  40   vibrations 


II  CHAXGE  OF  FOE.M  IX  MUSCLE  DURING  ACTIVITY  139 

per  sec.  •■  Wollaston  had  previously  attempted  to  determine  the 
^abration-frequency  in  vohmtary  contraction  of  his  brachial  muscles 
by  supporting  his  arm  on  a  grooved  hoard,  over  which  a  rounded 
piece  of  wood  passes  with  such  rapidity  that  the  sound  is  of  the 
same  pitch  as  the  muscle-sound.  He  found  that  the  frequency 
of  the  latter  lay  between  20  and  30  vibrations.  Helmholtz  sul)- 
sequently  found,  by  means  of  the  consonating  spring,  that  in 
voluntary  innervation  there  was  a  marked  and  visible  consonance, 
when  the  spring  was  registered,  at  18—20  vibrations  per  sec. 

It  would  appear  from  these  experiments  that  the  viljration- 
frequency  of  the  natural  muscular  rhythm  in  man  is  not  30-40, 
but  18-20.  What  is  heard  as  the  muscle-tone  is  really  only  the 
first  over-tone  of  the  true  muscle- vibration,  the  ground-tone  of 
which  is  no  longer  within  the  range  of  audible  perception ; 
according  to  Helmholtz  it  corresponds  wdth  the  C  of  the  16 -foot 
open  organ-pipe,  and  is  like  this  a  resonance-tone  of  the  ear. 
We  cannot  therefore,  from  the  pitch  of  the  sound  that  is  directly 
audible  in  voluntary  contraction  of  the  muscle,  draw  any  direct 
conclusions  as  to  the  frequency  of  the  central  impulses.  But  the 
objective  resonance  experiments  with  consonating  springs,  as  well 
as  the  observation  of  du  Bois-Eeymond,  to  the  effect  that  a  similar 
bruit  is  heard  both  in  voluntary  innervation  and  in  artificial 
tetanus  when  the  current  is  led  into  the  spinal  cord,  and  not 
directly  to  nerve  or  nniscle,  do  notwithstanding  appear  to  show 
tliat  the  natural  rhythm  of  excitation  from  the  central  nervous 
system  lies  at  about  18-20  per  sec.  According  to  du  Bois- 
Eeymond  we  heai,  under  these  conditions,  not  the  tone  of  the 
current  oscillations,  l;)ut  a  deeper  tone,  corresponding  in  every  way 
with  the  muscle-l)ruit.  Kronecker  and  Stanley  Hall  (3)  obtained 
the  same  results  from  the  objective  registration  of  variations  in 
bidk  of  the  exposed  M.  biceps  femoris  of  rabl)it,  by  means  of 
]\Iarey's  air-capsules.  In  agreement  with  the  results  of  Helmholtz 
and  du  Bois-Eeymond,  the  curve  descril;)ed  by  the  muscle  only 
showed  20  shallow  undulations,  when  the  number  of  stimuli 
led  into  the  spinal  cord  was  about  43  per  sec.  This  seems 
to  determine  objectively  that  the  central  organ  (spinal  cord)  not 
merely  possesses  an  intrinsic  rhythm  of  innervation  peculiar  to  it 
under  all  circumstances,  but  that  the  number  of  efferent  impulses 
also  corresponds  in  general  with  the  number  of  Adbrations  in  the 
natural  muscle-tone.     Horsley  and  Schafer  found  on  tetanising  the 


140  ELECTRO-PHYSIOLOGY 


cerebral  cortex  fillet,  or  spinal  cord,  that  the  I'ate  of  muscular 
vibration  was  much  lower,  the  average  of  vibrations  being  only 
10,  when  the  stimulation -frequency  was  above  10  per  sec; 
the  results  of  voluntary,  persistent  contraction  also  correspond 
with  this  lower  value,  and  Canney  and  Tunstall  (37)  determined 
the  same  in  man  (cf.  also  Griffiths,  38). 

V,  Kries  (39)  arrived  at  similar  results.  He  used  apparatus 
constructed  after  one  of  Marey's  sphygmographs  :  "  A  steel  spring- 
plate  is  fixed  at  one  end,  the  other  free  end  carries  on  one  surface 
a  wooden  peg  about  2  cm.  long,  to  which  is  fastened  the 
little  button — a  thin  disc  of  wood  1  cm.  in  diameter — that  rests 
on  the  muscle.  The  other  surface  of  the  steel  spring  is  provided 
with  a  sharp  edge,  which,  as  in  INIarey's  sphygmograph,  transfers 
the  movements  of  the  spring,  greatly  magnified,  to  a  very  liglit 
recording  lever."  AVhen,  after  fixing  the  arm,  the  hand  was  bent 
sharply  towards  the  wrist,  v.  Kries  obtained  curves  from  the 
flexor  muscles  of  the  under-arm  like  Fig.  62,  c,  with  a  distinct 
rhytlnuical  periodicity  of  11  "8  per  sec.  The  oscillations  of  tlie 
(jther  muscles  were  still  slower,  r.g.  the  deltoid  (weight  held  out 
with  arm  stretched  lioriz(jntally)  showed  a  rhythm  of  9 "6  per 
sec. ;  plantar  flexion  of  the  foot  only  7'7.  Hence  it  would 
appear  that  the  numl)er  of  impulses  hitherto  taken  as  tlie  rhythm 
of  central  innervation,  i.e.  18-20  per  sec,  is  too  high,  and  that 
with  slow  moNcments  or  persistent  contraction  it  must,  as  a  rule, 
be  estimated  at  10-12  per  sec.  But  as  v.  Kries  pointed  out, 
both  the  rhytlim  of  pliysiological  innervation  and  the  time- 
relations  of  the  single  impulse  must  vary  within  considerable 
limits,  for  the  persistent  contractions,  due  to  voluntary  innervation, 
are  effected  by  11—12  impulses  per  sec,  wliile,  on  the  other 
hand,  we  are  also  capable  of  making  11  single  movements  in 
a  second  (pianoforte  playing),  wliich  rhythm  must  also  necessarily 
be  present  in  the  innervation  process.  It  may  be  concluded 
that  in  both  cases — notwithstanding  the  coincident  j)erio(ls — the 
innervation  must  have  varied  considerably  (v.  Kries,  I.e.) 

As  was  remarked  by  Briicke  (28),  it  is  in  the  highest  degree 
improbable  that  voluntary  muscular  movements  are  due  to  only 
one  single  efferent  impulse  from  the  cerebrum.  In  all  cases, 
even  tlie  shortest  voluntary  "  twitch "  implies  a  short  tetanus. 
This  agrees  with  Barat's  statement  (14,  p.  26)  that  "a  voluntary 
contraction  of  the  simplest  possiljle  character  (tap  with  the  fingei) 


CHANGE  OF  FORM  IN"  MUSCLE  DURING  ACTIVITY 


141 


general!}^,  lasts  twice  as  long  as  the  same  movement  excited  by  a 
single  induction  shock."  Y.  Kries  confirmed  this,  and  was  also 
able  to  show  from  the  graphic  record  of  the  activity  of  the  flexor 
muscles,  with  the  quickest  possible  rhythmical  movements  of  the 
middle  finger  or  whole  hand  (9  per  sec),  minute  but  quite 
visible  oscillations,  accessory  to  the  larger  waves,  with  an  interval 
of  Jg- sec.  (Fig.  62,&). 

If  every  experimental  error  from  mechanical  vibration  is  here 
really  excluded,  we  must  inevitably  conclude  with  v.  Kries  that 
the  rhythm  of  increase  in  the  muscle,  as  in  other  cases,  indicates 
the  rhythm  of  the  central  impulses  that  impinge  upon  it.  With 
a  rapid  sequence  of  short  movements  we  should  therefore  have  to 
picture  the  process  of  innervation  as  such  "  that  our  will  presides 
over  combinations  of  stimuli  in  which  the  single  unpulses  follow 
with  great  rapidity,  one  predominating  in  each  case  over  the  rest 


Fig.  6-2.— Oscillations  witli  voluntary  muscle  activity.  «,  With  strenuous,  jjersistent  contraction 
of  muscles  of  the  forearm  (hand  balled  towards  the  fist)  ;  the  spring  rests  on  the  volar  side 
of  the  under-arm.  h,  Activity  of  flexor  muscles  on  rapid  rhythmic  bending  of  the  middle- 
finger,    (v.  Kries.) 

to  a  marked  extent."  The  extent  and  diversity  of  physiological 
reaction  in  quick  and  sluggish  muscle,  as  above,  are  closely  allied 
to  the  idea  that  along  with  slow  and  rapid  movements  there  is 
also  innervation  of  functionally  different  elements,  the  more  so  as 
partial  innervation  of  one  and  the  same  muscle  does  undoubtedly 
occur.  In  favour  of  such  a  view,  which  needs  much  farther 
investigation,  we  may  perhaps  quote  the  observation  of  v.  Kries 
that  the  highest  frequency  of  motor  impulses  occurs,  not  with  the 
development  of  the  greatest  power,  but  with  the  greatest  mobility. 
"  The  most  pronounced  efforts  were  produced  with  low  stimulation- 
frequency  (10-12  per  sec.)."  If  these  last  experiments  militate 
against  the  theory  that  there  is  a  constant  invariable  "  intrinsic 
rhythm  "  of  the  central  nervous  system,  this  is  no  less  the  case 
in  V.  limbeck's  observations  on  the  number  of  oscillations  yielded 
by  a  muscle  on  artificial  excitation  of  the  brain  or  spinal  cord  by 
induction  currents  of  alternating  frequency  (.30).      Both  in  warm- 


142  ELECTRO-PHYSIOLOGY 


blooded  animals  (dog,  rabbit)  and  in  those  that  are  cold-blooded, 
the  number  of  stimuli  acting  upon  the  central  organ  in  a  unit  of 
time  may  be  varied  witliin  wide  limits  without  interrupting  the 


v•vvv^^,•vv^.vvv^ArvV'J-^vvv^^-^v-nnn^v^rvTl'-|n^A'v/W<VWl^^^ 


'^vAA.V\A/s^^/\aaaaaaAaAAA/vAAAAA>\AAAAAAWWVu  ' 


Fig.  (i3.— Tetanus  curve  of  Rabbit  with  direct  excitation  of  spinal  cord.     The  stimulation-frequency 
varies  between  10  and  34  per  sec.    (v.  Limbeck.) 

uniform  rhythmical  oscillations  (longitudinal  or  lateral  variations) 
of  the  excited  muscle.  This  is  very  evident  in  the  accompanying 
curve  (Fig.  63) — obtained  by  direct  stimulation  of  the  spinal 
cord  of  rabbit — which  shows  most  plainly  how  the  number  of 
muscular  contractions  per  second  increases  with  the  number  of 
stimuli  sent  into  the  central  organ. 

The  stimulation -frequency  varied  in  this  case  between  10 
and  34,  with  prolonged  tension  of  the  spring  of  a  Neff's  hammer 
in  the  induction  apparatus,  the  correspondence  in  number  of 
the  single  contractions  (oscillations)  of  the  muscle  being  so 
exact  that  at  the  beginning  even  the  make  and  break  effects  are 
visible  in  the  curve,  as  shown  by  the  greater  and  lesser  indenta- 
tions.      The  same    results  appeared  from  other  experiments,  in 


Fig.  (34. — Muscular  oscillations  in  strychnia  tetanus  (Frog),    a,  Commencement ;  h,  end  of  the 
curve,     (v.  Limbeck.) 

which  a  persistent  reflex  contraction  of  the  muscle  was  obtained 
(central  excitation  of  sciatic  nerve  of  opposite  side).  V.  Limbeck 
failed  to  discover  oscillations  in  the  myogram  at  stimulation- 
frequencies  employed  by  Kronecker  and  Stanley  Hall  (43  per 
sec),  as  well  as  Horsley  and  Schiifer ;  the  curves  were  almost 


CHAXGE  OF  FORM  IX  MUSCLE  DURIXG  ACTIVITY  14-: 


unbrokeij.  On  tlie  other  hand,  l)oth  in  frog  and  rabl^it  very 
obvious  oscillations  (though  of  strikingly  different  rhythm)  were 
produced  by  strychnia  spasms.  Fig.  64  shows  that  they  vary 
in  the  frog  from  2  to  o   per  sec. :  Fig.  65  from  10  to  19  in  the 


Fig.  (35. — Strychnia  tetanus  of  Rabbit,    (v.  Limbeck.) 

rabbit.      Towards  the  end  of  the  spasm  the  oscillations  became 
gradually  less  frequent,  and  are  often  grouped  together  (Fig.  65). 


BiBLIOGEAPHY 

1.   Helmholtz.    Monatsber.  der  Berliner  Academie.     185-4.     p.  328. 
.,    ^.  Kries  f  Berichte  d.  naturforsch.  Ges.  zu  Freiburg.     2  Bd.     Heft  2.     1886. 
■■\Du  Bois  Arch.     1888.     p.  538. 

3.  KRO>rECKER  und  Hall.    Du  Bois  Arch.     1879.     Suppl. 

4.  Ch.  Eichet.    Physiol,  des  muscles  et  des  nerfs.     Paris  1882. 

f  r  Sitzuiigsber.  der  kais.  Acad,  der  "Wiss.  math. -phys.  Klasse.     79. 

I  S.  V.  Basch.  -      Abth.  III.     1879. 

5.  -i  l  Du  Bois  Arch.     1880.     p.  283. 

j  Kronecker.    Du  Bois  Arch.      1879,  p.  379  ;  und  1880,  p.  285  f. 
L  Ehrmann.     Med.  Jahrbiicher.     "Wien  1883.    p.  141. 

(5.   Engelmaxn.  (Pfl^^g^^-^^^-^^^-     29.     1882.     p.  453. 
I  Pfl tigers  Arch.     3. 

7.  Chr.  Bohr.    Du  Bois  Arch.     1882.     p.  233. 

8.  RoLLETT.     Denkschriften  der  math. -phys.  Klasse  der  kais.  Academie  der  "Wiss. 

in  Wien.     LIII.     p.  194  ff. 

9.  KoHNSTAMM.    Du  Bois  Arch.     1893.     \>.  125. 
fy.  Frey.     Du  Bois  Arch.     1887. 
Iv.  Kries.     Du  Bois  Arch.     1886. 

11.  Grutzner.     Pfliigers  Arch.     41  Bd.     p.  277. 

12.  V.  Fret.    BeitrJige  zur  Physiologic.     C.  Ludwig  zu  seinem  70.  Gebui-tstage  ge- 

•\vidmet  von  .seinen  Schiilern. 

13.  Ranvier.     Arch,  de  Physiol,  norm,  et  pathol.     1874. 

14.  Kronecker  und  Stirling.     Du  Bois  Arch.     1878.     \k  1. 

15.  GriItzner.     Breslauer  med.  Zeitschr.     1886.     Xo.  1. 

16.  A.  FiCK.     Pfliigers  Arch.     41  Bd.     p.  176  ff". 

(  Marey.     Travaux  du  Laboratoire.     2.     1876. 

j  Stromberg  und  Tigerstedt.     .Mitth.  vom  pliysiol.  Laborat.   zu  Stockholm. 

17.  -{      V.     1888. 

I  Dastre.     Jourii.  de  I'Anat.  et  de  la  Physiol.      1882. 

lGley.    Arch,  de  PhysioL     1890.     p.  439. 
/Ranvier.     Lecons  de  I'Anat.  gen.     1877-78.     p.  63. 
\H.  de  Varigny.    Arch,  de  Physiol.     1886. 
19.  Schoenlein.    Du  Bois  Arch.     1882.     p.  369. 


10 


18 


144  ELECTRO-PHYSIOLOGiY 


20.  Bernstein.   Unters.  liber  den  ErregungsYorgang  im  Nerven-  unci  Muskelsystem, 

Heidelberg  18/1.     p.  100  S. 

21.  Grtjnhagen.     Pfliigers  Arch.     YI.     p.  157. 

„^    „  f  Pfliigers  Arch.     lY.     p.  3. 

22.  Ekgelmann.   -{  ^„..^        .     ,        ,.,,TT  o-  A  1 

I  Pflugers  Arch.     XA  II.     p.  8o  Anmerk. 

23.  Roth.    Pfliigers  Arch.     42  Bd.     1888. 

24.  V.  Kpjes.     Yerhandl.  der  naturforsch.  Ges.  zu  Freiburg.  ,   YIII.       2. 

25.  SCHOENLEIN.     Du  Bois  Arch.     1882.     (Zur  JSTatur  der  Anfangszuckung.) 

26.  H.  Keaft.     Pfliigers  Arch.     44  Bd.     p.  353. 

27.  BiEDEKMANN.    Sitzuugsber.    der  Wiener  Acad.     XCI.     III.  Abth.     1885.     p, 

29  ff". 

28.  E.  Brucke.     Sitzungsber.  der  Wiener  Acad.      LXXY.     1877. 

29.  V.  Helmholtz.     Wiss.  Abhandl.     II.     p.  929. 

30.  T.  Limbeck.     Arch,  fiii-  Pathol,  und  exper.  Pharmakologie.     25  Bd.     p.  171. 

31.  Martins.    Du  Bois  Arch.     1883.     p.  571. 

32.  Hermann.    Handbuch  I.     1.     p.  51. 

33.  Bernstein.     Pfliigers  Arch.     11  Bd.     p.  191. 

34.  Ch.  Loven.     Du  Bois  Arch.     1881.     p.  363. 

^  f  Arch,  de  Physiol,  par  Brown-Sequard.     1891. 

30.     \^  EDENSKI.  I  ^^  g^.^  ^^^j^_       ^ggg_       p_   g^._ 

36.  HoRSLEY  und  Schafer.    Journ.  of  Physiol.     YII.     p.  96. 

37.  Canney  und  Tunstall.     Journ.  of  Pliysiol.     YI. 

38.  Griffitsh.    Journ.  of  Physiol.     IX.     p.  39. 

39.  V.  Kries.     Du  Bois  Arch.     1886.     Suppl. 


VIII. — Conductivity  of  Muscle 

A  remarkable  antithesis  may  in  general  be  observed  with  regard 
to  the  property  of  transmitting  localised  excitation,  between  the 
relatively  undifferentiated  plasma  of  the  Protozoa,  characterised 
by  flowing  (amoeboid)  movements,  and  the  contractile  ^&?"i/s  dif- 
ferentiated from  the  same.  In  the  former,  localised  and  strictly 
limited  excitation  usually  produces  local  effects  only,  in  the  most 
favourable  instances  distributed  merely  over  the  immediate 
vicinity,  whereas  in  the  differentiated,  fibrillar  parts,  conduction 
is  nearly  always  highly  developed.  In  the  majority  of  cases  it 
has  not  been  accurately  determined  whether  the  excitatory  move- 
ments due  to  "  cell-conductivity "  in  certain  plants  result  from 
the  transmission  from  cell  to  cell  of  the  exciting  stimulus 
(extension,  traction)  in  consequence  of  alterations  of  turgor — 
comparable  with  its  transmission  in  Carchesium  colonies  where 
the  individual  polyps  are  not  in  protoplasmic  continuity — or  of 
the  actual  excitatory  ■p'i'ocess  (alterations  of  the  plasma). 

In  the  latter  case  {e.g.  excitable  tissue  of  Mimosa)  this  would 
mean  an  extraordinary  rapidity  of  conduction  for  undifferentiated 


ir  CHANGE  OF  FORM  IN  MUSCLE  DURIX(;  ACTIVITY  145 

plasma,  the  more  so  since  the  mobility  of  the  plasma  in  vegetable 
cells  is  on  the  whole  but  little  developed,  and  stands  at  much  the 
same  level  as  that  of  the  free-swimming  Amreba. 

It  can,  however,  be  demonstrated  that  conductivity  increases 
pari  IX18SU  with  increased  mobility  and  sensibility  to  external 
stimuli — a  fact  of  which  we  have  unmistakable  evidence  in 
Protozoa,  on  comparing  the  sluggish  Ehizopods  with  the  highly 
mobile  Flagellates  and  Ciliata.  In  most  Infusoria  there  is,  on 
excitation,  a  specific  conduction  in  minute  motor  organs  (cilia, 
fiagellse),  which  must  be  regarded  as  a  fibrillar  differentiation  ; 
although  in  these  cases  the  body-plasma  itself  seems  to  be  the 
conductor  throuo-h  which  excitation  is  transmitted  with  extra- 
ordinary  rapidity. 

The  ciliary  movements  in  localised  excitation  of  Ciliata  belong 
to  this  category.  If,  e.g.,  Paramsecium  aurelia  encounters  any 
obstacle  in  swimming,  the  cilia  of  the  body  collectively  make  a 
stroke  almost  simultaneously  in  the  direction  opposed  to  the 
normal,  thus  jerking  the  animal  backwards,  after  which  the  original 
movement  begins  again.  A  similar  effect  on  the  cilia,  without 
simultaneous  co-operation  of  the  myoideum,  may  also  sometimes 
be  observed  in  this  protozoan. 

The  contraction  of  the  myoideum  itself,  the  simplest  muscle- 
element  known  to  us,  takes  place  as  a  rule  so  rapidly,  that  analysis 
of  its  time-relations  in  localised  excitation  is  impossible.  "  If, 
e.g.,  a  Spirostomum,  which  owing  to  its  extended  form  is  the  best 
adapted  to  this  kind  of  experiment,  is  locally  stimulated  at  one 
end  only,  contraction  of  the  whole  body  will  ensue,  without  any 
perceptible  difference  in  time  between  the  contraction  of  the 
anterior  and  posterior  ends."  "  Hence  it  may  be  concluded  that 
conductivity  of  excitation  within  the  myoideum  is  excessively 
rapid ;  the  effects  of  excitation  follow  immediately  on  the  weakest 
stimuli  without  any  perceptible  latent  period,  while  in  the  relatively 
undifferentiated  rhizopod  plasma  there  is  almost  invariably  a  pro- 
nounced time  of  latent  excitation  between  stimulus  and  visible 
effects  of  stimulation  "  (Verworn).  In  both  cases  the  myoideum 
reacts  precisely  like  the  most  highly  differentiated  striated  muscles, 
in  which,  however,  notwithstanding  the  rapidity  of  transmission, 
the  wave  of  contraction  can  be  exactly  measured.  We  are 
indebted  to  Aeby  (1)  for  the  first  experiments  in  this  direc- 
tion ;  he  used  the  graphic  method  to  determine  the  course  of  the 

L 


146 


ELECTRO-PHYSIOLOGY 


contraction  wave  in  two  different  points  of  the  muscle  (frog's 
gracilis).  In  the  case  of  a  muscle  with  parallel  fibres,  locally 
excited  at  one  end  only,  the  obvious  consequences  will  be  a  con- 
traction (expansion)  of  the  part  excited,  which  travels  at  great 


Pig.  66. — Velocity  of  contraction  wave  in  muscle.    The  magnitude  of  interval  between  the  two 
curves  (of  expansion)  is  the  measure.    (Marey.) 


speed  from  the  seat  of  excitation  along  the  entire  length  of  the 
muscle.  Two  given  points  in  the  continuity  of  the  muscle  will 
contract  at  different  times,  one  after  the  other,  and  thus  by  means 
of  two  levers,  each  of  which  rises  with  the  expansion  of  a  given 
section  of  the  muscle,  the  curve  of  expansion  in  both  sections  can 
be  recorded  upon  a  suitable  myograph  (Fig.  70).  From  the 
magnitude  of  the  interval  between  the  two  curves  standing  upon 
the  same  abscissa,  it  is  easy  to  calculate  the  rapidity  at  which  the 
wave  of  contraction  is  transmitted  (Fig.  66). 

Similar  results  to  those  of  Aeby 
were  obtained  by  v.  Bezold,  1861 
(2),  but  with  quite  a  different  method. 
He  lixed  a  muscle  with  parallel  fibres 
lightly  between  two  corks  at  its 
centre,  so  that  direct  transmission  of 
changes  in  form  was  prevented,  but 
not  the  propagation  of  the  excitatory 
process  ;  the  lower  part  only  (Fig.  67) 
recorded  its  contraction,  and  thus 
the  time  elapsing  between  an  ex- 
citation at  the  upper  end,  and  the  beginning  of  the  twitch  at 
the  lower,  was  determined  ;  this  would  obviously  correspond  with 
the  rapidity  of  transmission  from  the  excited  point  to  the  first 
section  beyond  the  clamp.  The  experiments  of  Aeby  and  v. 
Bezold  gave  the  rapidity  of  transmission  in  striated  frog's  muscle 


Pig.  67. — Rate  of  transmission  of  excita- 
tion in  muscle,     (v.  Bezold's  method.) 


CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY 


147 


as  about  1  m.  per  sec.  (l"2-l-6  m.),  but  later  investigations 
found  a  much  higher  velocity.  Bernstein,  e.g.  (3),  gives  a  velocity 
of  3 •2-4-4  ms.,  on  measuring  the  latent  period  of  the  curve 
of  expansion  in  a  given  section  of  the  muscle  (gracilis  and 
semimembranosus  group  in  frog)  when  excitation  was  applied 
directly  to  the  spot  recording  itself,  and  subsequently  at  as  great 
a  distance  from  it  as  possible.  The  experiment  was  arranged  as 
in  Fig.  68.     It  will  be  seen  to  consist  in  a  modification  of  Aeby's 


Fig.  68. — Rate  of  transmission  of  excitation  in  muscle.     (Bernstein's  method.) 

method,  in  which,  however,  it  is  not  so  much  the  velocity  of  trans- 
mission of  the  contraction  idcivc,  as  the  underlying  excitation,  that 
is  measured,  its  value  being  taken  as  identical  with  the  former. 

As  the  gracilis  and  semimembranosus  muscles  used  by  Aeby 
and  Bernstein  are  characterised  by  a  very  oblique  tendinous 
intersection,  so  that  each  muscle  consists  as  it  were  of  two  com- 
pletely separate  portions,  in  which  excitation  remains  isolated 
under  all  conditions,  it  seemed  advisable  to  repeat  the  experi- 
ments with  more  suitable  preparations.  Hermann  (4)  accord- 
ingly employed   tlie  two    sartorius   muscles    of  a  curarised  frog 


148 


ELECTRO-PHYSIOLOGY 


laid  closely  together,  and  determined  the  rapidity  of  transmission 
to  be  from  2  to  7  ms.  From  this  experiment  of  Bernstein,  the 
duration  and  length  of  an  entire  wave  of  contraction  are  easy  to 
determine.  If  a  muscle  of  sufficient  length  could  be  procured,  we 
should  be  able,  on  exciting  one  end  of  the  muscle,  to  follow  the 
progress  of  the  contraction  wave  with  the  unaided  eye.  This  is 
prevented  by  the  shortness  of  the  muscle  preparations  practicable  ; 
but  on  the  hypothesis  that  a  muscle  consists  of  physiologically 
homogeneous  fibres,  we  have  in  the  curve  of  expansion  of  any 
section  an  approximately  correct  picture  of  the  process  and  dura- 
tion of  the  wave  of  contraction,  or  more  correctly  of  the  altera- 
tion in  condition  of  the  muscular  elements,  while  the  wave  of 
contraction  is  sweeping  over  them.  The  duration  of  the  curve 
described  therefore  coincides  with  the  vibration  period  of  the 
wave  of  contraction.  The  rapidity  of  this  wave  being  known,  its 
length  also  may  be  calculated.      When  the  wave  w  (Fig.  69)  is  at 


Fig.  60. 


the  point  represented  in  the  diagram,  it  has  already  passed  the 
point  of  excitation  ^9 ;  while  at  ^;,  however,  it  has  been  trans- 
mitted as  far  as  /.  If  its  duration  be  termed  {D),  its  length  (L), 
and  the  rapidity  of  transmission  ( V),  L  —  VD.  According  to 
Bernstein's  experiments,  the  value  of  (Z)  is  between  198  and 
380  mm. 

In  contractile  substances  whose  conductivity  of  excitation  has 
been  little  developed,  as,  e.g.,  in  Rhizopoda  {Dijffiugia),  it  is  at  once 
evident  on  exciting  locally  that  the  resulting  changes  are  most 
pronounced  in  the  immediate  neighbourhood  of  the  point  of 
excitation,  and  become  weaker  in  proportion  as  they  spread  by 
conduction  (Verworn,  5).  On  touching  a  pseudopodium  of  Difflugia 
gently  with  the  point  of  a  needle,  the  manifestations  of  excitation 
(wrinkling,  and  extrusion  of  substance)  are  strictly  localised.  If  the 
stimulus  is  strengthened,  "  the  phenomena  extend  over  the  entire 
pseudopod,  and  are  much  more  rapid  and  vigorous  after  repeated 
excitation,  so  that  the  greater  part  of  the  pseudopod,  and  eventually 


II  CHAXGE  OF  FORM  IK  MUSCLE  DURIKd  ACTIVITY  149 

the  whole  of  it,  is  retracted.  The  more  distant  pseudopodia,  how- 
ever, still  remain  unaffected,  or  retract  only  a  very  little,  and  that 
gradually."  Finally,  with  very  strong  stimulation,  the  process  of 
contraction  may  extend  to  all  the  pseudopodia,  till  the  whole 
mass  is  withdrawn.  "  The  stimulated  pseudopod  is  drawn  back 
most  quickly,  almost  instantaneously,  while  the  others  follow 
more  slowly  in  proportion  with  their  distance.'' 

It  follows  that  stronger  stimuli  not  only  produce  a  quicker 
reaction  than  weak  stimuli,  but  that  the  effects  are  more  widely 
diffused,  i.e.  the  effect  diminishes  with  distance  from  the  point  of 
excitation. 

Although  it  is  a  ■priori  probable  that  the  same  is  true  of 
conduction  of  every  excitatory  process  in  all  living  substance, 
its  direct  proof  is  very  difficult  wherever  excitability  and 
conductivity  are  highly  developed,  since  the  difference,  owing 
to  the  inconsiderable  length  of  the  tracts  available,  must  be 
minimal.  This  notwithstanding,  Bernstein  succeeded  in  demon- 
strating that  the  wave  of  contraction  in  striated  frog's  muscle 
undergoes  a  perceptible  diminution  (a  "  decrement ")  during  its 
course,  whence  it  follows  that  the  expansion-curve  of  a  clirectly 
excited  point  of  the  muscle  is  invariably  higher  than  that 
of  a  more  distant  point  excited  with  the  same  stimulus.  It 
must,  however,  be  remembered  that  these  experiments  relate  to 
excised  muscles,  in  which  nutrition  is  no  longer  normal,  so 
that,  as  du  Bois-Eeymond  pointed  out,  the  decrement  observed 
might  well  be  a  manifestation  of  the  dying  muscle.  And,  indeed, 
we  shall  see  from  certain  galvanometric  effects  in  uninjured 
muscle,  to  be  discussed  below,  that  a  decrease  in  the  excitation 
wave  preceding  the  wave  of  contraction  is  not  perceptible. 

In  view  of  the  significant  differences  in  velocity  of  the 
contraction  process  in  striated  muscles  of  different  animals,  and 
even  in  different  muscles  of  the  same  species,  it  is  not  surprising 
that  similar  differences  should  exist  in  regard  to  conductivity, — the 
muscular  twitch  being  in  general  only  the  expression  of  a  contrac- 
tion spreading  itself  from  the  point  of  excitation  over  the  entire 
muscle.  Accordingly  the  rapidity  with  which  excitation,  or  con- 
traction, is  transmitted  varies  in  the  same  instances  and  the  same 
sense  as  the  curve  of  the  twitch,  so  that  its  rapidity  may  be  said  to 
vary  directly  with  the  magnitude  of  the  latter.  According  to  Her- 
mann and  Aeby  the  velocity  in  the  tortoise  averages  0'5-l"S  m. ; 


150 


ELECTRO-PHYSIOLOGY 


and  since  this  refers  to  the  rapidly-moving  M.  retractor  of  the 
neck,  the  other  muscles  of  the  same  animal  must  yield  a  still 
lower  value.  Bernstein  and  Steiner  (6)  found,  as  we  should 
expect,  that  the  rate  of  conductivity  in  warm-blooded  muscles 
(sterno- mastoid  of  dog)  was  considerably  greater  than  in  cold- 
blooded animals  (3—6  m.),  and  certain  experiments  of  Hermann 
{infra)  estimate  it  for  living  human  muscle  at  between  10  and 
13  m.  per  sec. 

We  are  indebted  to  Eollett  (7)  for  experiments  on  the  rapidity 
of  transmission  of  contraction  in  the  red  and  pale  muscles  of 
rabbit,  which  notably  present  wide  differences  in  regard  to  the 


Fig.  70. — Detennination  of  velocity  of  muscular  excitation  by  the  pince  niyoyni-Xihique.    (Marey.) 

time -relations  of  their  twitches.  After  freeing  the  pale  semi- 
membranosus and  the  red  cruralis,  he  placed  a  strip  30—40  mm. 
long  between  the  forceps  of  a  Marey 's  2^incs  myogra2jMque  (Fig.  70). 
These  were  connected  with  a  Marey's  registering  tympanum,  by 
means  of  which  the  curves  of  expansion  were  recorded  on  a  rotat- 
ing cylinder,  which  also  showed  a  tuning-fork  tracing  of  100 
vibrations  per  sec.  A  make  induction  shock  served  as 
stimulus.  The  animals  experimented  on  were  curarised.  The 
curve  of  expansion,  corresponding  with  the  excitation  point,  is 
again  steeper  and  less  extended  than  the  transmitted  wave,  so 
that  in  estimating  the  time  differences  between  the  curves 
the  interval  at  which  they  commence  is  the  only  datum.  The 
physiological  deviations   of   the  pale  (quick)   and   red  (sluggish) 


II  CHANGE  OF  FORM  IX  MUSCLE  DURING  ACTIVIT^'  151 

muscles  are  also  exhibited  here  in  regard  to  duration  of 
expansion,  which  is  greater  at  the  excitation  point  of  the 
cruralis  than  in  semimembranosus.  The  rate  of  transmission  per 
second  in  the  latter  is  5417—11,364  mm.,  in  the  former  3000— 
34,000  mm.  The  value  of  the  red  (sluggish)  rabbit  muscle 
therefore  tallies  with  the  rate  of  transmission  (3500  mm.  per 
sec.)  determined  by  Bernstein  and  Steiner  for  the  nictitating 
muscle  of  the  dog.  And  if  comparative  observations  on  the  velo- 
city at  which  excitation  is  transmitted  in  the  striated  muscles  of 
different  animals  thus  establish  a  close  ratio  between  the  dying- 
out  of  the  contraction-process  at  any  point  and  the  rapidity  of  its 
conduction,  the  same  appears  no  less  clearly  from  the  fact  that  in 
a  muscle  preparation,  where  the  length  of  twitch  is  altered 
experimentally  in  a  i^lvs  or  minus  sense,  the  rate  of  conductivity 
is  equally  affected  by  the  same  data,  e.g.  in  particular,  fatigue 
(death),  and  alterations  of  temperature. 

As  in  warm-blooded,  striated  muscles  the  length  of  twitch 
and  general  excitability  diminish  more  rapidly  after  any  injury 
than  in  those  that  are  cold-blooded,  so  with  conductivity- — only  in 
a  much  more  pronounced  degree ;  for  it  is  always  this  property 
which  is  the  first  to  suffer,  and  even  to  disappear,  at  a  time  when 
local  excitability  can  still  be  easily  demonstrated.  The  further 
investigation  of  these  manifestations  of  decline  in  warm-blooded 
muscles  presents  many  points  of  interest.  Since  the  rate  of  con- 
ductivity diminishes  constantly,  and  more  rapidly  than  excitation, 
we  seem  to  have  at  hand  a  simple  means  of  following  the  wave 
of  contraction  with  the  unaided  eye  without  artificial  assistance. 
Schiff  (8)  was  the  first  to  demonstrate  that  local  mechanical 
excitation,  applied  shortly  after  the  death  of  the  animal  to  an 
exposed  muscle,  produces  a  swelling  which  remains  stationary, 
while  tw^o  waves  of  contraction  spread  almost  at  the  same  moment 
on  either  side  to  both  ends  of  the  muscle.  "  While  the  contraction 
is  proceeding,  the  parts  adjacent  to  the  now  pronounced  swelling 
relax.  If  the  wave  of  contraction  has  reached  the  end  of  the 
muscle,  it  turns  back  towards  its  starting-point.  But  in  the  mean- 
time a  new  wave  has  started  from  the  point  of  excitation  in  both 
directions,  which  encounters  the  reflected  wave  and  crosses  it,  and 
this  interference  repeats  itself  frequently,  because  each  wave  after 
crossing  runs  on  undisturbed  till  eventually  it  grows  weaker  and 
dies  out."      As  the  muscle  becomes  more  and  more  moribund,  and 


152  ELECTRO-PHYSIOLOGY 


loses  its  conductivity  in  proportion,  the  play  of  waves  jfinally  ceases 
altogether,  although  the  persistent  contraction  still  remains  at  the 
point  of  excitation,  and  was~  by  Schiff  regarded  as  the  specific 
manifestation  of  muscular  excitability,  and  opposed  as  the  "  neuro- 
muscular "  twitch  to  the  "  idio-muscular  "  contraction.  This  local 
swelling  appears  most  plainly  on  mechanically  excitating  (by  a 
blow,  or  stroking  with  a  blunt-pointed  instrument)  the  moribund 
muscle  of  a  dead  animal,  which  no  longer  twitches  with  electrical 
stimulation.  "  The  swelling  appears  slowly,  and  is  delayed  in 
proportion  with  the  exhaustion  of  the  muscle  and  length  of  time 
elapsed  since  the  death  of  the  animal."  When  the  swelling  has 
reached  its  maximum  it  maintains  it  for  a  longer  or  shorter  time, 
perhaps  several  minutes,  and  then  diminishes  again  comparatively 
slowly.  In  this  way,  especially  when  stroking  at  right  angles  to 
the  direction  of  the  fibres,  it  is  possible  to  write  and  draw  with  a 
hard  object  on  the  upper  surface  of  a  suitable  muscle. 

Distinct  idio-muscular  swellings  can  seldom  be  provoked  in 
fresh  frog's  muscle.  The  sartorius  from  a  half-dried  leg  works 
better  according  to  Hermann  (9).  "  If  such  a  muscle  is  stretched 
out  on  cork  at  a  certain  stage,  every  contact  of  a  needle,  especially 
with  gentle  cross -pressure,  will  produce  a  local  swelling,  which 
persists  for  some  time.  The  same  reaction  is  even  better  shown 
on  cooled  frog's  muscle,  in  which  both  mechanical  and  electrical 
excitation  produce  a  long -sustained  contraction  at  the  point 
stimulated.  The  contractile,  palatine  organs  (containing  striated 
muscle -fibres)  of  certain  fishes  (cyprinoids,  tench)  also  exhibit 
well-marked,  idio-muscular  swellings. 

These  observations  of  Schiff,  which  may  be  compared  with  the 
older  experiments  of  Bennet  Dowler  (Hermann's  Handb.  i.  1,  p. 
45,  note)  on  the  muscles  of  the  human  subject  immediately  after 
death,  were  subsequently  confirmed,  and  extended  in  several 
directions,  though  the  original  interpretation  of  Schiff — to  which 
Klihne  also  subscribed  later — to  the  effect  that  the  phenomena 
were  merely  the  consequences  of  diminished  excitability  in  the 
muscle,  appeared  somewhat  dubious.  The  observations  mainly 
refer  to  the  appearance  of  the  "  idio-muscular  "  swelling,  and  the 
slowly-transmitted  wave  of  contraction  that  proceeds  from  it  in 
the  muscles  of  the  living  human  subject.  After  E.  H.  Weber, 
Ed.  Weber,  and  Funke  had  exhibited  upon  themselves,  by  hitting 
the  biceps  or  gastrocnemius  with  a  blunt  surface,  idio-muscular 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  153 

swellings  which  exactly  resembled  those  on  the  muscles  of  the 
decapitated  subject  (a  mode  of  demonstration  to  which  Kiihne 
subsequently  referred  as  "  familiar  to  every  gymnast "),  L.  Auer- 
bach  followed  up  these  effects  more  thoroughly,  and  communicated 
his  observations  in  an  essay,  "  Ueber  topische  Muskelreizung," 
published  in  the  Jahresberichfen  d.  Sehlessisclien  Gesellsckaft, 
1861  {Nat.  Wiss.,  Med.  AUheilg.,  Heft  3).  He  produced  local 
excitation  by  blows  with  a  percussion  hammer,  and  reported  that 
very  generally  in  man,  and  in  many  muscles  of  the  body,  an 
almost  conical  lump  rises  up  on  the  spot  thus  percussed,  lasting 
as  a  rule  3-5  sees,  with  comparatively  no  alteration,  and  then 
sinking  slowly  down  again  at  the  same  point  of  the  muscle.  He 
refers  some  minor — apparently  local — changes  of  the  lump  to  the 
collective  shortening  of  the  muscle-bundle  from  the  mechanical 
excitation.  In  many  "  rare  "  cases  (Auerbach  quotes  four  such 
individuals)  there  is,  moreover,  an  undulatory  manifestation,  but 
he  was  only  able  to  induce  it  in  pectoralis  major  and  the  inner 
half  of  biceps  by  smart  taps  on  a  spot  overlying  the  bone.  This 
wave-like  appearance  consists  of  a  low  crest  rising  up  on  either 
side  of  the  idio-muscular  swelling,  which  gradually  spreads  like  a 
wave  on  the  surface  of  smooth  water,  at  very  moderate  velocity, 
towards  the  two  ends  of  the  muscle.  He  never  observed  a  back- 
ward motion  of  these  waves  in  the  human  subject.  On  the 
other  hand,  it  was  very  conspicuous  in  the  rabbit,  where  he  was 
able  to  provoke  Schiff's  play  of  waves  on  most  muscles  by  gentle 
mechanical  stimulation,  e.g.  tapping,  or  stroking  vertically  with  a 
blunt  object.  According  to  A.  Pick,  the  most  favourable  muscles 
are  the  ventral  section  of  pectoralis  major,  and  the  sterno-mastoid. 
On  stroking  these  muscles  vigorously  with  the  handle  of  a  scalpel 
across  the  direction  of  the  fibres,  a  linear  swelling  appears  at  the 
excited  point,  after  a  brief  twitch  of  the  muscle-bundle,  while  a  flat, 
slowly-transmitted  wave  spreads  towards  the  intersection  of  the 
muscle  in  one  or  both  directions  from  the  seat  of  excitation.  After 
death  this  undulatory  contraction  always  disappears  before  the 
idio-muscular  swelling,  which  can  still  be  provoked  several  hours 
later.  Sometimes  the  swelling  seems  to  bifurcate  by  the  formation 
of  a  hollow  at  the  point  excited,  while  a  wave  spreads  out  on 
both  sides  towards  either  end  of  the  muscle,  and  may  eventually 
be  reflected  back  again.  The  same  has  been  observed  in  the 
living  human  subject  by  Baierlacher  (12).      Both  these  experi- 


154  ELECTRO-PHYSIOLOGY 


ments,  and  those  of  Erb  (13)  on  highly- excitable  convalescents 
after  severe  illnesses  {e.g.  phthisical  subjects  and  others,  in  whom 
a  tap  on  certain  skeletal  muscles  produces  a  definite  swelling, 
whence  little  waves  of  contraction  extend  to  both  ends  of  the 
muscle-fibres),  go  to  prove  that  these  manifestations  are  due  not 
so  much  to  depressed  excitability  of  the  muscle  as  to  normal 
effects  of  excitation,  which  Auerbach  regards  as  the  direct  ex- 
pression of  excessive  excitability.  Analogous  observations  of 
Chwostek  (14)  and  Pick  {I.e.)  on  patients  (mostly  lean,  badly- 
nourished  individuals)  seem  to  indicate  that  the  idio-muscular 
swelling  may  be  regularly  provoked  in  man,  if  not  in  all  muscles 
or  by  every  mechanical  stimulus.  Biceps  brachii  and  the  flexor 
group  of  the  fore-arm  seem  particularly  suited  for  the  purpose. 
A  firm  support  is,  as  may  be  supposed,  conducive  to  the  appear- 
ance of  an  effect  of  excitation,  and  the  advantages  of  it  are  seen 
in  exciting  an  appropriate  muscle  of  any  animal  with  uniform 
excitation  before  and  after  supporting  it  firmly.  It  is  possible 
that  the  formation  of  the  swelling  in,  e.g.,  the  lower  limbs  of  very 
wasted  subjects  only,  much  more  rarely  on  normal,  healthy 
individuals, — may  depend  less  upon  a  definite  excitatory  state 
of  the  muscle  than  upon  the  fact  that  such  muscles  are 
more  favourable  to  the  action  of  a  mechanical  stimulus.  It 
is  noticeable  that  under  all  conditions  when  the  undulatory 
contraction  appears  along  with  the  idio-muscular  swelling,  the 
muscle  is  still  capable  of  twitching,  so  that  the  seime  fibres 
could  transmit  raind,  as  ivell  as  sloio,  waves  of  eoniraetion.  The 
same  is  exhibited,  as  Kiihne  showed  {I.e.  p.  618),  in  perfectly 
fresh  frog's  muscle.  Indeed,  the  manifestation  is  much  more 
regular  there  than  in  the  muscles  of  warm-blooded  animals.  If 
the  sartorius  is  hung  up  by  one  end,  and  a  cross-section  made  at 
the  other  with  scissors,  at  the  same  time  somewhat  stretching  the 
muscle,  "  so  that  the  play  of  waves  is  not  lost  in  retrograde 
twitches,  the  little  waves  will  be  seen  in  transmitted  light,  in 
which  the  muscle  exhibits  beautiful  colours,  apparently  rising  in 
the  transparent  mass,  and  subsiding  again,  so  that  there  is  a 
lively  alternation  of  play  of  colour  in  the  shimmering  mu.scle." 

Hermann  (9,  p.  604)  made  similar  observations  on  the  freshly- 
prepared  sartorius,  fixed  to  a  cork-plate,  and  mechanically  excited 
at  any  point  by  sticking  in  a  needle,  or  pressing  down  a  fine 
wooden  chisel.      From  this  point  a  minute  wave  or  ripple  usually 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  15f. 

spreads  over  the  fibres  in  both  directions  from  the  point  excited, 
lasting  as  a  rule  a  little  longer  than  the  excitation.  Under 
these  conditions  there  can  be  no  question  of  referring  the 
phenomenon  to  diminished  muscular  excitability.  It  appears 
indeed  from  Milrad's  (15)  experiments  upon  muscles  of  which 
the  excitability  had  been  raised  or  depressed  by  different  chemical 
substances  (veratrin,  chloroform,  IsTa^COg,  caffein)  that  the 
appearance  of  the  idio-muscular  swelling  is  favoured  by  diminution 
of  excitability,  and  delayed  by  its  augmentation,  provided  the 
difference  between  the  normal  and  the  poisoned,  or  fatigued,  muscle 
is  insignificant,  and  does  not  often  exceed  the  error  of  observa- 
tion, but  that  the  slow  undulatory  contractions  are  only  apparent 
with  normal  or  increased  excitability.  Both  Schiff  and  Auerbach 
state  that  the  play  of  waves  on  stroking  with  a  blunt  needle 
appears  only  in  the  muscles  of  freshly-caught  frogs,  and  Milrad 
says  that  this  form  of  contraction  may  nearly  always  be  produced 
if  excitability  is  artificially  heightened,  or  abolished  if  it  is  lowered. 
Since  both  the  idio-muscular  swelling  and  the  wave-action  may 
be  observed  in  curarised  animals,  they  are  obviously  the  con- 
sequence of  direct  muscular  excitation,  although  on  many  sides 
the  theory  has  been  put  forward  (chiefly  on  the  ground  of  totally 
inadequate  experiments,  1 6)  that  the  motor  nerve-endings  take 
part  in  the  muscle  phenomenon  under  discussion. 

Although  mechanical  stimuli  are  undoubtedly  the  most  favour- 
able to  the  production  of  the  idio-muscular  swelling,  the  applica- 
tion of  other  stimuli  is  by  no  means  excluded.  Auerbach,  e.g.  {I.e. 
p.  342),  found  that  with  local  application  of  "weak"  faradisation 
currents  a  lump  was  raised  at  either  pole,  while  with  stronger 
currents  there  was  a  marked  swelling  over  the  whole  intra- 
polar  area,  as  was  afterwards  confirmed  by  Milrad  {I.e.  p.  266). 
And  further,  we  must  regard  the  persistent  closure  contraction 
{infra)  which  appears  at  the  kathode  on  sending  in  a  constant 
current  of  sufficient  strength  in  both  striated  and  smooth  muscle, 
as  an  idio-muscular  swelling,  while  the  wave  of  striated  muscle 
(Hermann's  galvanic  wave),  that  may  be  seen  to  proceed  from 
the  anode  under  similar  conditions,  seems  to  be  directly  com- 
parable with  the  wave-action  on  mechanical  excitation. 

As  Eollett  (7,  p.  201  ff.)  correctly  pointed  out,  the  muscles  of 
insects  must  have  an  especial  significance  re  interpretation  of 
relations  between  the  contraction  wave   and  the  manifestations 


156  ELECTRO-PHYSIOLOGY 


which  appear  in  different  forms  of  muscular  contraction. 
Bowman  first  made  observations  on  these  muscles,  and  his 
results  tally  exactly  with  the  preceding.  Here  we  find  an  un- 
dulatory  contraction  in  the  individual,  living  or  surviving, 
musde-Jibrcs,  which  may  be  directly  observed  with  the  micro- 
scope, and  thus  (as  also  from  the  excessive  slowness  of  the 
process)  exhibit  minutiae  that  must  always  escape  us  in  the 
entire  muscle,  where  we  have  numerous  fibres  in  very  different 
physiological  conditions.  It  is  further  possible  to  fix  such  short 
contractions  during  their  course,  by  treatment  with  proper 
methods  of  hardening,  so  that  the  finest  details  of  the  changes 
which  accompany  the  process  of  contraction  in  the  muscle-fibres 
become  visible.  Even  during  life  two  processes  of  movement 
may  be  observed  in  the  striated  muscles  of  many  insects,  those 
which — corresponding  with  the  twitch  of  vertebrate  muscles — con- 
sist in  the  rapid,  instantaneous  contraction  of  the  muscle-bundle 
in  toto,  and,  on  the  other  hand,  knots  or  short  waves  spreading 
slowly  over  the  fibres,  which  often  arise  periodically  or  rhythmic- 
ally with  no  demonstrable  external  stimulus.  Here  again  it  is 
important  to  note  that,  as  Wagener  (17)  pointed  out  with  regard 
to  the  larva  of  Corethra,  the  fibres  in  which  this  wave-action  is 
apparent  were  perfectly  capable  of  producing  total  contractions 
(twitches).  He  repeatedly  saw  both  forms  of  movement  alterna- 
ting in  the  same  fibre,  to  which,  however,  it  must  be  added  that 
the  wave -action  does  not  appear  in  perfectly  vigorous  animals. 
Laulanie  (18),  who  investigated  Corethra-larvse  in  every  possible 
stage  of  dying,  also  makes  a  sharp  distinction  between  the  muscular 
movements  of  the  vigorous  animal  and  those  of  the  surviving 
muscles  of  the  dying  animal.  He  regards  the  former  ("  secousses, 
contractions  totales  et  simultanees  ")  as  the  expression  of  normal 
muscular  activity  ;  the  latter  ("  ondes  musculaires  ")  as  the  expres- 
sion of  intrinsic  activity  in  the  surviving  muscles.  Eollett  (19) 
subsequently  analysed  both  phenomena  more  exactly.  He 
described  the  undulations  of  the  muscles  of  dying  Corethra-larv?e 
as  follows :  "  The  waves,  at  first  few  in  number,  in  single  fibres 
of  the  muscle  visible  only  under  the  microscope,  gradually  appear 
in  more  and  more  of  the  fibres,  and  then  repeat  themselves  in 
the  same  fibres  at  ever-shorter  periods,  so  that  a  lively  undulation 
ensues,  which  only  dies  away  after  a  long  time,  as  it  came.  The 
waves  in  the  single  fibres  repeat  themselves  only  at  longer  periods, 


II  CHANGE  OF  FOR:\r  IX  MUSCLE  DURING  ACTIVITY  V.u 

the  number  of  fibres  in  which  waves  occur  grows  less  and  less, 
and  after  a  time  there  are  only  a  few,  in  which  they  spread 
at  longer  and  longer  intervals,  until  finally  they  appear  in  single 
fibres  at  very  remote  periods." 

Since,  as  Eollett  also  affirms,  the  first,  slowly  -  spreading 
waves  appear  in  fibres  that  are  still  capable  of  total  contractions 
(twitches),  it  cannot  be  doubted  that  the  short  waves  also  must 
be  regarded  as  "  peculiarly  distributed  processes  of  movement 
in  normally  active  muscular  substance,  produced  by  specific 
excitation."  These  waves  in  the  muscles  of  dying  Corethra- 
larvse,  present  the  greatest  similarity  with  the  movements  of 
freshly-excised  insect  muscles,  as  frequently  observed  since  the 
researches  of  Bowman  (20).  Eollett  studied  these  in  long, 
narrow  strips  of  muscle  from  a  great  number  of  beetles,  in  which 
the  undulatory  movement  often  lasted  for  hours.  It  usually 
reaches  its  maximum  development  at  the  first  moment,  where 
the  particles  of  muscle  are  quickly  examined  under  the  micro- 
scope. Here,  too,  the  waves  appear  as  short  knots  rising  and 
falling  steeply,  and  spreading  slowly  in  the  fibres,  and  their 
length  also  is  limited,  including  only  from  about  12  to  24  strite. 
This  limitation  continues  when  the  undulatory  motion  becomes 
less  energetic,  which  happens  again  in  this  case,  because  the 
waves  appear  in  fewer  and  fewer  fibres  at  longer  intervals,  and 
finally  only  at  prolonged  periods  in  single  fibres.  If  freshly-excised 
beetle  muscle  is  covered  quickly  and  examined  under  the  micro- 
scope, a  lively  undulation  is  seen  to  be  spreading  over  the  fibre, 
l)ut  we  are,  as  Eollett  says,  quite  ignorant  as  to  the  cause  of  the 
undulations.  They  spread  along  the  fibres,  coming  and  going 
always  in  the  same  direction.  Yet  this  is  not  invariably  the 
case.  Sometimes  a  definite  starting-point  of  the  advancing  wave 
occurs  in  the  middle  of  the  individual  fibre.  This  was  demon- 
strated by  Bowman,  and  later  by  Aeby,  on  the  transparent  legs 
of  certain  small  kinds  of  spiders.  A  swelling  appears  on  the 
given  point,  which  (cf.  Aeby)  appears  to  rest  for  a  moment  on 
the  crest  of  its  progress,  and  then  suddenly  divides  in  such  a 
way  that  the  most  swollen  part  sinks  rapidly  back  to  the  original 
level,  while  the  two  halves  separate  and  spread  in  opposite 
directions  towards  both  ends  of  the  fibre  ;  where  such  a  spot  has 
once  been  found,  it  is  easy  to  see  that  it  forms  for  some  time 
a     permanent     starting  -  point     for    new,    periodic     undulations. 


158  ELECTRO-PHYSIOLOGY 


According  to  EoUett,  it  appears  as  though  the  short  waves,  in 
many  cases,  arise  in  or  near  a  section,  from  which  inferences 
may  be  made  as  to  the  significance  of  the  muscle-current,  or  tlie 
chemical  changes  concomitant  with  the  death  of  the  muscle- 
substance,  as  a  discharging  excitation.  In  individual  cases  the 
end-plate  can  undoubtedly  constitute  the  point  of  departure  for 
a  wave  of  contraction,  and  this  apparently  applies  to  all  the 
waves  developed  along  one  fibre. 

EoUett  tried  to  determine  the  rate  of  transmission  of  these 
waves  in  sufficiently  long  strips  of  muscle  cut  out  of  the  extensors 
and  flexors  of  the  hind  pair  of  legs,  in  large  beetles,  using  the 
same  method  which  E.  H.  Weber  employed  to  measure  the 
rapidity  of  the  capillary  circulation.  The  number  of  metronome 
beats  was  counted  for  the  interval  between  the  coincidence  of 
the  maximum  with  a  given  fraction  of  the  scale,  at  the  beginning, 
and  at  the  end,  of  an  ocular  micrometer.  Values  were  thus 
obtained  of  0*0 8-0 '6 7  mm.  (average,  0*169  mm.);  the  length 
of  the  waves  varied  between  0'08  and  0-115  mm.  Thus  there 
are  true  "miniature  waves,"  which  propagate  themselves  at 
such  a  low  rate,  that  even  the  slowest  waves  of  contraction  in 
striated,  vertebrate  muscle,  varying  according  to  Auerbach 
from  314  to  371  mm.  per  sec,  have  a  considerable  velocity 
in  comparison.  Unfortunately  it  has  till  now  been  found 
impossible  to  measure  the  rate  of  conductivity  of  the  excitation 
which  provokes  the  rapid  twitch  in  insect  muscles.  But  it 
is  certain  that  it  must  be  considerable  in  twitches  of  short 
duration  (0-011 2-0-527  sees.,  Eollett),  even  on  Eollett's 
assumption,  that  the  longest  waves  (transmitted  at  greatest 
velocity)  of  insects  are  far  behind  those  of  vertebrate  muscle. 
Schiff  and  others,  as  we  have  seen,  observed  a  reficction  of  the 
slow  contraction  wave  in  many  striated,  vertebrate  muscles,  when 
it  reached  the  end  of  a  fibre.  A  similar  effect  seems  seldom,  if 
ever,  to  appear  in  insects ;  Eollett  at  least  has  failed  to  discover, 
either  in  the  entire  muscle  of  Corethra  -  larvai,  or  in  excised 
beetle  muscle,  anything  "that  could  be  described  as  a  reflected 
wave." 

Both  in  the  case  {supra)  in  which  the  wave  arises  in  the 
centre  of  a  fibre,  and  spreads  to  both  sides,  and  in  that  where  no 
definite  point  of  departure  is  to  be  discovered,  it  may  be  seen 
to  disappear   suddenly,  midway,   with    no    previous    diminution. 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  159 

Interference  between  two  waves  of  contraction  coming  from 
opposite  sides  (the  two  terminal  sections  of  a  fibre)  was  only 
once  observed  by  Eollett,  when  the  two  waves  at  first  united 
into  one  larger  wave  and  then  expired. 

The  "  fixed  "  waves  of  contraction,  described  above,  are  due 
(as  appears  probable  from  Eollett,  19)  to  a  kind  of  summation  ; 
they  may  frequently  be  observed  in  the  muscle-fibres  of  insects 
killed  in  alcohol  and  osmic  acid.  They  are  usually  distinguished 
from  the  waves  of  living  muscle  by  their  greater  length,  which 
Engelmann  explains  on  the  supposition  that  they  were  fixed 
while  their  rapidity  of  transmission  was  still  considerable. 

Eollett,  however,  assumes  that  "  an  entire  series  of  short, 
consecutive,  living  waves  were  partially  fixed  in  succession,  so  that 
they  do  not  represent  any  single  process,  but  are  the  sum  of 
fixed  parts  of  contraction  waves  in  time  order.  If  any  given 
point  of  the  muscle-fibre  has  for  some  time  been  the  starting- 
point  of  short  periodic  waves,  some  of  the  contracted  muscle 
sections  will  frequently,  as  Eollett  says,  remain  fixed,  while  the 
adjacent  muscle -sections  on  either  side  relax  again.  Thus  a 
persistent  contraction  is  produced  in  a  short  segment  of  the 
muscle  only,  and  from  this  the  remaining  waves  spread  outwards. 
And  it  must  be  observed  that  each  new  wave  that  originates 
from  the  contracted  section,  itself  gives  rise  to  one  similar  section, 
while  the  rest  relax  again ;  in  this  way  the  area  of  fixed  con- 
traction grows  longer  and  longer,  till  at  last  tlie  whole  movement 
is  blocked,  or  ceases  with  a  wave  that  dies  out  against  the  relaxed 
end  of  the  fibre."  Such  fixed  waves  can  rarely  be  demonstrated 
on  the  muscles  of  vertebrates,  in  which  waves  of  contraction  may 
of  course  be  seen,  but  not  the  lively,  persistent,  spontaneous 
undulation  (Bowman,  I.e.;  Nasse,  21).  Doyer's  expansion  is  very 
commonly  the  starting-point  of  undulation  in  insect  muscle,  and 
accordingly,  the  spot  at  which  fixed  waves  of  contraction  are 
readil}^  formed.  Sometimes  partial  contraction  is  exhibited,  the 
so-called  lateral  waves  (ondes  laterales)  of  fixed  contraction. 
Eollett  assigns  this  as  a  special  characteristic  of  most  Chry- 
somelid  (7,  p.  216)  muscle-fibres,  while  in  other  insect  muscles 
lateral  waves  of  contraction  occur  rarely  {Tenehrionidas,  Citr- 
ridionidm,  and  Scarahoiidai).  The  nerve-ending  of  the  Chrysome- 
lides  seems  to  present  a  special  point  of  departure  for  a  physio- 
logical reaction  which  occurs  with  1  y  osmic  acid,  and  alcohol,  or 


160  ELECTRO- PHYSIOLOGY 


a  process  set  up  by  these  reagents,  before  they  have  had  time  to 
affect  the  muscle-substance  itself,  the  proof  being  that  the  lateral 
contraction  corresponding  with  the  nerve -end  plate  appears 
immediately  before  the  death  of  the  fibres  implicated.  Generally 
speaking,  all  that  has  been  said  of  the  development  of  the  "  fixed  " 
waves  applies  to  the  origin  of  the  lateral  waves  also. 

Summing  up  the  preceding  observations,  the  main  con- 
clusion is  that  the  cross-striated  muscle-fibres  of  vertebrates, 
as  well  as  of  invertebrates,  possess  the  faculty  of  conducting 
long  and  short,  rapidly  and  slowly  transmitted,  waves  of 
contraction,  which  apparently  depend  upon  differences  of  excita- 
tion only.  With  regard  to  the  normal  function  of  muscles  as 
locomotor  organs,  the  short  waves  can  have  but  little,  if  any,  signi- 
ficance. This  only  makes  them  theoretically  the  more  interesting. 
The  enormous  differences  in  rate  of  transmission  render  it  at  first 
sight  questionable,  whether  we  are  really  dealing  in  both  cases 
with  the  same  elements  of  the  muscle-fibres,  since  no  perceptible 
differences  in  velocity  of  conduction  have  experimentally  been 
found  to  correspond  with  the  differences  of  intensity  within  the 
range  of  excitation  required  to  provoke  a  twitch ;  nor  can  the 
"quick"  and  "sluggish"  muscle-fibres  contribute  to  the  explanation, 
since  the  differences  which  they  exhibit  in  rapidity  of  contraction 
and  conductivity  are  quite  inadequate  to  explain  the  disparity. 
On  the  other  hand,  we  turn  almost  involuntarily  to  the  two 
chief  constituents  of  every  muscle-fibre,  sarcoplasm  and  fibrils. 
We  know  that  in  many  instances  the  protoplasm  (sarcoplasma) 
from  which  the  twitching  fibrils  have  been  differentiated,  is  not 
wholly  wanting  in  intrinsic  contractility ;  many  ciliated  Infusoria, 
e.g.,  have  the  property  through  the  myoideum,  not  only  of  twitch- 
ing, but  also,  by  contraction  of  the  body-plasma,  of  making  sluggish 
movements,  approximating  to  the  amoeboid  type.  The  possibility 
that  the  formative  plasma  of  the  muscle-fibres  in  higher  animals 
also  may  exhibit  contractility  can  the  less  be  doubted,  since  on 
many  sides  (Klihne)  the  fibrils  are  regarded  as  passive,  elastic 
elements,  whose  main  function  is  the  elongation  of  the  muscle. 
Even  if  this  extreme  view  cannot  be  admitted  to  correspond  with 
the  facts,  it  is  equally  out  of  the  question  to  disregard  the  possi- 
bility of  contractility  in  the  sarcoplasm.  Granting  this,  however, 
it  would  appear  from  all  analogies  that  the  relations  between 
excitability  and  conductivity  in  the  two  elementary  constituents 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  161 

of  each  muscle  -  fibre,  present  fundamental  differences,  in  the 
sense  that  the  fibrils  conduct  much  more  quickly  (contract  by 
"  twitches  "),  while  the  less  excitable  sarcoplasm,  like  almost  all 
undifferentiated  protoplasm,  transmits  the  excitation  -  process 
slowly.  On  histological  grounds  it  is  indeed  impossible  not  to 
regard  the  fibrils  as  co-operating  generally  in  the  slow  waves 
of  contraction,  but  it  is  noticeable  that  the  undulation  in  the 
muscle-fibres  is  best  exhibited  under  just  those  conditions  which 
have  been  found  experimentally  to  favour  the  excitation  of 
non-differentiated,  contractile  plasma.  Mechanical  excitation  is 
particularly  appropriate,  so  that,  at  least  in  vertebrate  muscles, 
the  intensity  of  excitation  must  be  much  greater  than  is  required 
to  provoke  a  twitch.  The  time-order  of  development  in  the 
different  forms  of  contraction  is  also  to  be  noticed,  since  it 
occasionally  gives  an  opportunity  of  observing  how  the  twitch 
that  immediately  succeeds,  and  almost  coincides  with,  the  stimulus, 
is  followed  by  the  idio-muscular  swelling,  from  which  again  pro- 
ceed the  slowly-spreading  undulations.  This  agrees  with  the 
much  greater  latent  period  and  slower  development  of  contraction, 
in  purely  plasmatic  parts.  The  question  touched  on  here  will 
only  be  decided  when  our  knowledge  of  the  functional  relations 
between  sarcoplasm  and  fibrils  has  advanced  much  further  than 
at  present. 

In  the  cases  so  far  discussed  we  have  been  concerned  exclu- 
sively with  conduction  of  the  excitatory  process  within  single, 
multinudear,  longitudinal  cells,  such  as  those  of  striated,  skeletal 
muscle-fibres.  A  wave  of  contraction  either  stops  half-way  or 
spreads  to  the  end  of  the  fibre,  from  which  it  can  eventually 
be  reflected  back,  or  more  frequently  expires  there.  Every 
tendinous  intersection,  however  small,  will  entirely  block  the 
transmission  of  even  the  strongest  excitation,  so  that  stimulation 
of  a  polymerous  muscle  at  one  end  only  results  in  contraction 
of  the  part  directly  implicated.  It  is  equally  impossible  for 
excitation  to  be  ti'ansmitted  transversely  from  one  fibre  to  the 
next  adjacent,  and  any  seeming  exceptions  {e.g.  in  drying  muscle) 
are,  as  we  shall  see,  to  be  explained  on  other  grounds.  The 
conduction  of  excitation  in  muscular  organs  consisting  of  uni- 
nuclear onuscle- cells  is,  on  the  other  hand,  fundamentally  different. 
Co-ordinated  action  of  a  number  of  muscle-cells  in  consequence 
of  local  stimulation  is  obviously  possible  only  where  the  excita- 

M 


162  ELECTRO-PHYSIOLOGY  chap. 

tion  is  conveyed  by  nerves,  or  where  it  transmits  itself  from  cell 
to  cell  by  direct  propagation.  Both  alternatives  seem  actually  to 
be  present. 

In  the  heart,  Engelmann  (22)  was  the  first  to  investigate 
these  relations,  A.  Fick  (23)  having  previously  made  a  short 
communication  on  the  subject.  If  a  resting  frog's  ventricle, 
separated  from  the  auricle,  is  stimulated  at  any  given  point, 
a  general  contraction  (systole)  of  the  hollow  muscle  follows,  so 
that  the  excitation  must  have  been  distributed  uniformly  in 
all  directions  from  the  point  of  stimulation  by  conductivity. 
Engelmann  showed  that  the  ventricle  need  not  necessarily  be 
uninjured ;  the  experiment  succeeds  well  if  the  ventricle  of  a 
freshly -killed  frog  is  divided  by  scissors  into  two  or  more  pieces, 
connected  only  by  a  minute  bridge  of  muscle-substance ;  after  a 
time  all  the  pieces  will  contract  successively  when  any  one  of 
them  is  stimulated.  It  is  quite  indifferent  at  what  point  each 
bit  is  joined  to  the  others,  the  only  essential  is  that  they  should 
be  united  by  muscular  substance.  The  experiment  in  this  form, 
therefore,  indicates  "  that  excitation  can  be  transmitted  in  the  ven- 
tricle from  any  point,  to  any  other  point,  by  any  given  point." 
The  complete  conductivity  of  the  separate  muscle  bridges,  which 
is  disturbed  at  first,  comes  back  gradually  after  a  certain  time  has 
elapsed — perhaps  an  hour  or  longer.  If  a  bit  of  the  ventricle  is 
left  in  connection  with  the  beating  auricle,  this  bit,  when  con- 
ductivity has  been  fully  re-established,  will  contract  first  after 
each  auricular  systole,  then  the  next,  and  so  on.  The  contraction 
is  propagated,  therefore,  in  a  peristaltic  direction  from  base  to 
apex  of  the  ventricle.  If  the  preparation  is  no  longer  beating 
spontaneously,  the  succession  in  which  the  individual  pieces 
contract  will  depend  only  on  which  piece  was  first  excited,  since 
the  contraction  proceeds  from  this  successively  to  all  the  others  ; 
no  part  is  ever  omitted.  Since  we  are  a  2y'^iori  forbidden  on 
histological  grounds,  as  well  as  from  the  low  velocity  of  excita- 
tion, to  assume  that  each  cell  is  united  with  its  neighbours  by 
nerve-fibres,  the  second  view  only  is  admissible,  i.e.  that  excitation 
(contraction)  proceeds  directly  from  cell  to  cell  in  the  same 
manner  as  within  each  single  cell. 

The  time-relations  of  the  process  of  contraction  have  already 
been  described,  in  so  far  as  concerns  the  "  twitch "  of  cardiac 
muscle.      It  only  remains  to  consider  the  rate  of  conductivity. 


II  CHANGE  OF  FOKM  IN  MUSCLE  DURING  ACTIVITY  163 

i.e.  the  rapidity  with  which  the  excitation  is  transmitted  from 
section  to  section.  Under  normal  conditions  the  velocity  is  so 
great  in  the  frog's  heart  that  all  points,  as  in  the  excitation  of 
striated  skeletal  muscle,  seem  to  contract  simultaneously.  This 
effect  may  persist  in  a  fresh,  vigorous  heart,  even  when  the 
ventricle  has  been  cut  up  into  several  pieces.  As  a  rule,  how- 
ever, the  undulatory  process  of  the  contraction  can  then  at  once 
be  recognised.  It  often  seems  as  though  conduction  was  slower 
in  the  bridges  than  in  the  larger  pieces,  for  each  of  the  latter 
seems  to  contract  together,  as  a  whole,  while  a  perceptible  time 
elapses  between  the  contraction  of  two  successive  pieces.  Engel- 
mann  estimated  the  average  rate  of  conductivity  in  strips  of 
muscle  10—15  mm.  long  (snipped  out  of  the  ventricle)  at  about 
30  mm.  per  sec,  or  more  usually  10  —  20  mm.,  measured  by 
a  metronome,  giving  beats  at  ^  sees.  Although  these  values 
must  be  considerably  below  the  normal,  we  may  conclude  from 
them  that  even  in  the  most  favourable  cases  the  rate  of  conduct- 
ivity must  be  lower  than  it  is  when  the  excitation  is  transmitted 
by  nerve.  The  rate  of  transmission  is  diminished  to  a  striking 
degree  by  cooling  the  preparation.  Cooling  from  17°  to  50°  C, 
e.g.,  is  sufficient  to  reduce  it  from  20  to  8  mm.  Under  normal 
conditions  the  excitation  is  invariably  transmitted  from  auricle 
to  ventricle.  Engelmann  (22)  has  recently  ascertained  that 
muscular  conduction  is  in  this  case  the  sole  factor,  by  experi- 
ments on  the  "  suspended "  frog's  heart,  arranged  on  the  same 
principle  as  that  employed  by  Helmholtz  to  measure  the  rapidity 
with  which  the  excitation  of  nerve  is  transmitted.  The  auricle  to 
some  extent  represents  the  nerve,  the  ventricle  the  muscle ;  the 
former  was  excited  at  different  distances  from  the  ventricle,  and 
the  latent  period  of  the  ventricular  systole  in  each  case  was 
measured.  If  conduction  was  effected  by  nerve-fibres,  the  short- 
ness of  the  strips  employed  would  render  any  perceptible  difference 
improbable,  whereas  with  cell-conduction  in  the  muscle  it  was 
to  be  expected.  As  a  matter  of  fact,  a  very  considerable  retarda- 
tion was  observed  in  the  commencement  of  the  ventricular 
systole,  when  the  auricle  was  excited  at  a  greater  distance.  In 
a  given  case,  in  which,  however,  the  rapidity  was  no  longer 
perfectly  normal,  the  delay  amounted  to  0*09  sec,  corresponding 
to  a  rate  of  conductivity  of  90  mm.  per  sec.  But  this,  as 
Engelmann  pointed  out,  is  a  value  300   times   lower  than  the 


164  ELECTRO-PHYSIOLOGY  chap. 

rapidity  of  transmission  in  motor  frog's  nerves  under  the  same 
conditions.  Hence  it  would  appear  as  if  muscular  conduction 
from  auricle  to  ventricle  could  be  as  certainly  established  as 
within  the  auricle  and  ventricle.  However  much  the  magnitude 
of  the  velocity  of  muscular  excitation  may  depend  on  different 
states  of  the  muscle  (fatigue,  temperature),  it  can  be  maintained 
under  some  conditions  notwithstanding  considerable  alterations 
in  the  muscle-substance.  Thus  it  would  appear  that  with  partial 
turgescence  of  the  frog's  sartorius,  the  tracts  affected  may  com- 
pletely lose  the  power  of  contracting,  without  to  any  extent 
suffering  in  regard  to  electrical  sensibility,  or  conductivity 
(Biedermann,  24).  The  same  applies,  according  to  Engelmann 
(I.e.),  to  the  muscle  bridges  of  the  auricle  in  the  frog's  heart, 
which,  "  after  complete  abolition  of  their  contractility,  are  still 
able  to  transmit  the  motor  stimulus  to  the  ventricle,  and  that 
with  the  same  rapidity  as  if  the  power  of  contracting  was 
uninjured."  ^ 

It  cannot  be  doubted  that  the  same  relations  of  conductivity 
of  excitation  described  above  for  the  frog's  heart,  obtain  in  the 
cardiac  muscle  of  higher  vertebrates,  and  this  is  of  the  more 
consequence  since  there  is  in  general,  e.g.  in  mammals,  a  much 
less  extensive  contact  of  the  separate,  short,  and  broad  muscle-cells, 
which  really  unite  only  by  their  blunt  end-surfaces  and  short 
lateral  branches.  Similar  relations  exist,  again,  in  the  intestine  of 
insects  and  myriapods,  the  walls  of  which  contain  anastomosing, 
striated  (uninuclear)  muscle -cells,  which  by  contraction  set  up 
the  normal,  peristaltic  movements  of  the  digestive  tract.  Engel- 
mann (25)  considers  the  intestine  of  the  fly  to  be  the  most 
suitable  object  for  combined  anatomical  and  physiological  investi- 
gation, more  particularly  the  opening  of  the  end  of  the  intestine, 
from  the  mouth  of  the  Malpighian  tubules  to  the  rectum.  "  The 
muscular  integument  here  consists  essentially  of  a  single  layer  of 
strong,  striated  circular  fibres,  enclosed  within  an  unmistakable  sar- 
colemma  (invariably  absent  in  cardiac  muscle-cells),  and  separated 
by  perceptible  spaces  from  another."  Each  fibre  seems  to  be 
joined  to  its  neighbours  by  one,  or  several,  oblique  or  sometimes 

^  Kaiser  {Zeitschr.  f.  Biologie,  1894)  has  recently  criticised  the  cogency  of  the 
evidence  in  these  experiments,  and  refers  the  effects  observed  to  current  diffusion. 
This  can  only  be  ascertained  by  further  experiment,  for  which  we  have  not  yet  had 
opportunity. 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  165 

transverse  branches,  by  means  of  which  the  contractile  sul^stance 
all  along  the  end  of  the  intestine  is  woven  into  a  physiological 
continuity.  If  the  last  posterior  segment  of  a  fly  is  torn  away 
with  forceps,  the  end  of  the  intestine  will  usually  be  left  hanging 
from  it,  and  if  examined  while  fresh  in  0-5  ^  IsTaCl  solution, 
exhibits  lively  peristaltic  movements  :  peristaltic  waves  run 
every  few  seconds  at  tolerably  regular  intervals  from  the  mouth 
of  the  Malpighian  tubes  towards  the  rectum.  The  waves  at  first 
spread  so  quickly  that  it  is  impossible  to  detect  the  details  of 
the  process.  But  if  the  preparation  is  left  for  a  quarter  to  half 
an  hour,  or  pressed  down  witli  a  tolerably  heavy  cover-glass,  the 
contraction  is  transmitted  more  and  more  slowly,  the  waves  follow 
at  longer  intervals,  and  may  be  clearly  seen  to  spread  themselves 
over  the  single  fibres  and  connecting  processes.  "  If,  shortly 
after  a  wave  of  contraction  has  reached  the  lower  end  of  the 
opening  of  the  intestine,  this  end  is  mechanically  stimulated  with 
the  point  of  a  needle,  an  anti-peristaltic  wave  instantly  runs  up 
the  fibres  of  the  muscle,  to  the  opening  of  the  Malpighian  tubes, 
if  not  previously  arrested  by  meeting  a  wave  spreading  from 
above  downwards."  It  is  also  noticeable  that  the  conductivity 
of  the  contractile  substance  itself  appears  to  be  temporarily  much 
depressed  by  the  process  of  contraction.  A  wave  starting  after 
a  long  rest  spreads  with  apparently  uniform  rapidity  from  its 
point  of  departure.  But  if  another  wave  had  immediately  pre- 
ceded it,  the  new  excitation  only  produces  a  localised  contraction, 
or  at  most  a  wave  that  quickly  diminishes  and  dies  out  near  its 
starting-point. 

The  intestinal  tract  of  some  Fishes  {Tench,  Cohitis)  is  well 
known  to  contain  a  similar  arrangement  of  striated  muscle-fibres; 
whether  there  are  analogous  relations  of  conductivity  also  has  not 
yet  been  determined  (26).  On  the  other  hand,  the  conductivity 
of  the  contractile  tissues  of  certain  Medusae  {e.g.  Aurclia)  has  been 
thoroughly  investigated,  with  results  in  complete  accordance  with 
those  yielded  by  cardiac  muscle  (27). 

The  multiform  coiiviJlexes  of  smooth  muscle-cells  exhil)it  com- 
plete agreement  with  these  mononuclear,  striated  muscle-cells, 
in  regard  to  conductivity  of  excitation.  Here,  again,  it  is  to 
Engelmann  (28)  that  we  owe  the  most  important  conclusions. 
The  ureter  of  many  mammals  (rabbit,  guinea-pig,  rat,  etc.)  is 
jDeculiarly  suited  to  exact  investigations,  as  it  offers  a  delicate 


166  ELECTRO-PHYSIOLOGY  chap. 

muscular  integument,  about  1'3  mm.  thick  in  the  rabbit,  which 
extends  from  the  hilum  of  the  kidney  to  the  bladder,  along  the 
psoas  muscle,  with  a  surface  of  about  11  cm.  The  muscular 
sheet,  which  lies  between  the  adventitia  and  the  mucous  membrane, 
consists  of  a  thin,  internal,  longitudinal  layer,  and  an  external,  and 
much  thicker,  circular  layer.  Both  are  composed  of  smooth,  non- 
membranous,  mononuclear  fibre-cells,  about  0*2  mm.  long,  in 
which  hardly  any  perceptible  outline  can  be  detected  in  the 
physiologically  fresh  condition.  The  muscularis,  therefore,  gives 
the  impression,  even  under  a  high  power,  of  an  almost  homogene- 
ous, transparent  mass.  It  is  only  in  the  moribund  condition 
that  fine  stripe — the  optical  expression  of  the  cell-borders — 
appear  between  the  pale  nuclei.  Within  the  connective  tissue 
of  the  adventitia  there  is  a  ramification  of  nerves,  consisting  for 
the  most  part  of  pale  fibres  (Engelmann's  "Grundplexiis"),  in  which 
there  is  a  remarkable  and  complete  absence  of  nerve-cells.  Engel- 
mann  states  that  the  number  of  nerve-endings  within  the  mus- 
cularis is  much  less  than  that  of  the  smooth  muscle-cells.  This 
point,  however,  requires  further  investigation  with  the  recently 
discovered  methods,  which  would  very  probably  reveal  a  great 
abundance  of  nerves. 

As  a  rule  the  ureter  that  has  been  cautiously  exposed 
exhibits  spontaneous  waves  of  contraction,  spreading  peristaltically 
at  intervals  (mostly  from  10  to  20  sees.)  from  the  kidney  to  the 
bladder.  "  If  a  definite  point  is  taken  anywhere  along  the 
ureter,  a  weak,  momentary  dilatation  may  usually  be  seen 
at  the  segment  implicated  just  before  its  constriction,  after 
which  it  becomes  thin,  cylindrical,  and  much  paler.  At  the 
same  time  the  ureter  moves  perceptibly  downwards  (towards 
the  bladder).  The  velocity  with  which  the  waves  of  contraction 
spread  is  so  low  that  it  can  easily  be  determined.  T*his  is 
effected  either  by  counting  the  beats  of  a  metronome  set  at  -^ 
or  ^  sec,  during  the  time  at  which  the  wave  of  contraction  is 
transmitted  from  one  point  of  the  ureter  to  another  (one  being 
determined  close  to  the  kidney,  the  other  at  a  more  distant  spot, 
by  two  operators),  or  they  record  with  a  Marey's  tambour  the  con- 
tractions of  two  points  remote  from  one  another  upon  the  ureter. 
With  a  vigorous  rabbit,  at  sufficiently  high  temperature,  the 
velocity  was  20-30  mm.  per  sec;  in  the  cat  and  rat  it  appeared 
somewhat  greater  "  (Engelmann). 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  167 

With  artificial  (mechanical)  stimulation  the  contraction  is 
transmitted  from  both  sides  of  the  point  excited,  while  in  regard 
to  velocit}'  no  perceptible  difference  between  the  peristaltic 
and  anti-peristaltic  waves  can  be  determined.  It  is,  however, 
remarkable  that  the  contraction  only  appears  ivith  direct  excita- 
tion of  the  muscularis.  "  Neither  by  pressure  of  the  mucous 
membrane,  or  adventitia  with  the  nerve -plexus,  nor  of  the 
greater  nerve-trunks  at  the  hilus  and  bladder,  can  a  contraction 
be  discharged  anywhere  in  the  ureter.  Local  excitation  always 
produces  localised  contraction,  spreading  slowly  on  both  sides.  If 
the  ureter  is  divided,  crushed,  or  tied  at  any  point  of  its  length,  a 
contraction  will  occur  above  or  below  the  spot  after  every  excita- 
tion, and  is  transmitted  on  both  sides  of  the  excited  part,  but 
never  passes  beyond  the  dead  point.  Since  even  short  excised 
strips  of  the  ureter  react  peristaltically  when  excited,  we  cannot 
assume,  in  view  of  the  structure,  that  ganglion-cells  are  respon- 
sible for  the  appearance  of  the  peristalsis ;  the  ureter  rather 
reacts  to  mechanical  excitation  in  every  case  "  as  though  it  were 
a  single,  gigantic,  hollow  muscle-fibre."  We  have  already  seen  what 
an  extraordinary  influence  temperature  has  upon  excitability  and 
conductivity  in  the  ureter,  as  well  as  the  extraordinary  vitality  of 
muscles  that  are  deprived  of  normal  nutrition.  Each  wave  of 
contraction  produces  a  temporary  depression  of  excitability  and 
conducti\'ity  in  the  sheet  of  muscle,  from  which  it  only  recovers 
during  the  subsequent  diastole  and  interval  (just  as  in  the  striated 
muscle-nets  of  insect  intestine).  Every  diminution  of  conduct- 
ivity expresses  itself  by  the  gradual  disappearance  of  the  wave 
of  contraction,  which,  whether  spontaneous,  or  artificially  excited, 
becomes  weaker  in  proportion  with  the  length  of  its  course,  and 
finally  dies  out  even  in  immediate  proximity  to  the  point  of 
excitation.  Finally,  instead  of  the  advancing  wave,  there  is  left 
only  a  protracted  contraction  in  the  part  immediately  adjacent  to 
the  point  of  excitation — the  analogue  of  the  idio-muscular  con- 
traction in  striated  muscles.  The  rapidity  with  which  movement 
is  transmitted  varies  with  the  conductivity,  as  is  clearly  and 
easily  shown  by  cooling  and  warming.  Since  every  wave  of 
contraction  affects  the  time-relations  of  the  succeeding  wave,  it  is 
a  matter  of  course  that  if  the  spontaneous  contractions  succeed 
one  another  at  irregular  periods,  those  which  are  preceded  by  a 
short  pause  are  transmitted  more  slowly  than  those  which  follow 


168  ELECTEO-PHYSIOLOGY  chap. 

at  a  longer  interval ;  as  is  naturally  still  more  easy  to  demonstrate 
with  artificially  excited  waves  of  contraction.  It  is  evident  that 
immediately  after  the  passage  of  a  wave  of  contraction,  the  con- 
ductivity is  entirely  abolished,  and  only  recovers  its  original 
proportions  a  comparatively  long  time  after.  In  the  rabbit  the 
first  stage  lasts  for  over  a  second  under  normal  conditions,  and 
with  diminution  of  excitability  may  be  prolonged  to  5,  10,  or 
15  sees.  With  normal  conditions,  normal  conductivity  is  re- 
established, at  most,  1 0  sees,  after  the  passage  of  a  contraction. 

The  slowness  of  the  entire  process  of  excitation  constitutes  an 
easy  and,  we  may  say,  direct  means  of  determining  the  length  of 
the  contraction  wave  in  the  ureter,  if  the  approximate  duration 
of  the  contraction  is  multiplied  by  its  velocity.  If  we  reckon  the 
first  at  about  ^  sec,  the  other  at  33  mm.,  the  wave-length  comes 
out  at  1  cm.,  a  value  which  is  tolerably  constant,  since  we  find 
experimentally  that  the  alterations  in  duration  of  contraction  are, 
within  a  wide  range,  inversely  proportional  with  the  simultaneous 
alterations  in  the  rate  of  conductivity.  These  results  tally  with 
direct  observation,  since  the  length  of  the  contraction  wave  can 
be  immediately  determined  on  the  exposed  ureter. 

On  a  ureter  that  is  free  from  fat  and  somewhat  hyperaBmic, 
it  is  easily  seen  that  with  each  contraction  a  strip  of  about  1 
cm.  long  becomes  pale  in  toto,  and  progresses  in  undulations 
with  the  constriction.  The  pallor  is  generally  most  marked  at 
the  middle  of  the  strip,  the  ureter  sometimes  appearing  almost 
white ;  the  normal  gray-pink  colour  then  returns  by  degrees  on 
either  side.  If  anything  may  be  concluded  from  this  as  to  the 
magnitude  of  contraction  in  the  single  cross-sections,  it  would 
follow  that  shortening  and  relaxation  of  the  muscle-substance  of 
the  ureter  proceed  with  equal  velocity  (Engelmann). 

It  will  be  seen  from  the  above  that  a  whole  series  of 
facts  bearing  on  the  relations  and  conduction  of  the  contraction 
process  may  be  immediately  demonstrated  on  the  part  in  question, 
while  in  striated  muscle  the  finest  artificial  means  have  to  be 
employed  for  their  detection — a  point  which  we  shall  have  to 
insist  on  later.  For  the  moment  we  need  only  refer  to  the 
weighty  question  as  to  the  manner  in  which  the  conductivity 
of  excitation  (contraction)  is  effected  in  the  organ — which  is 
composed  of  innumerable  individual  cells  united  by  cement - 
substance. 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  169 

Seeing  that  mechanical  excitation  of  the  muscular  coat 
produces  contraction,  when  applied  to  any  point  of  the  ureter, 
which  proceeds  from  either  side  of  the  excited  spot  with  a 
rapidity  a  thousand  times  less  than  the  velocity  of  excitation  in 
nerve ;  and  further,  that  peristaltic  and  anti-peristaltic  propa- 
gation of  the  movement  are  exhibited  in  all  parts  of  the  ureter 
after  excision,  only  one  view,  as  Engelmann  stated,  is  admissible : 
the  peristaltic  and  anti-peristaltic  propagation  of  the  movement  is 
due  to  the  fact  that  excitation  is  transmitted  directly  from  cell  to 
cell  in  the  muscle  ivithout  intervention  of  ganglion-cells  or  nerve-fibres. 
In  other  words :  the  ureter  in  its  normal  state  is  'physiologically  « 
single,  hollow,  organic  muscle-fihre.  Eecent  investigations  into  the 
anatomical  connections  of  smooth  muscle-cells  give  consistent  sup- 
port to  this  view,  inasmuch  as  they  indicate  continuity  at  least  of 
the  sarcoplasm,  if  not  of  the  fibrils  also.  But  the  first  is  sufficient  if, 
we  can  hardly  doubt,  the  sarcoplasm  can  transmit  excitation  from 
fibril  to  fibril.  "  Plasma  bridges  "  indeed  become  superfluous,  since, 
as  Engelmann  correctly  observes,  there  is  nothing  to  prevent  such 
close  contact  of  the  naked,  sheathless,  living  fibre-cells,  that  they 
form  a  physiological  continuity.  This,  however,  admits  that 
a  molecular  effect  may  propagate  itself  in  the  ureter  in  cdl 
directions  from  its  point  of  origin.  Similarly,  of  course,  we  may 
imagine  the  process  of  conductivity  within  the  plexus  of  the 
striated  muscle-cells.  In  these  parts — consisting  of  smooth,  or 
striated,  uninuclear  muscle -cells — we  are  dealing  with  an 
organisation  of  cells,  each  individual  of  which  is  similarly 
co-ordinated  in  function,  like  the  other  excitable  cell-aggregates 
of  plants  and  animals  with  which  we  are  acquainted.  Indeed, 
we  are  reminded  almost  involuntarily  of  the  co-ordinated  activity 
of  ciliated  cells,  which  can  be  shown  experimentally  to  stand  in 
close  internal  relations  of  conductivity,  although  the  individual 
elements  appear  anatomically  to  be  even  more  distinct  than  the 
cells  of  smooth  muscle.  Here,  at  all  events,  no  protoplasmic 
bridges  have  been  demonstrated,  although  they  unquestionably 
exist  in  many  smooth  muscles,  as  well  as  in  excitable  vege- 
table-tissues. It  appears,  however,  that  in  all  such  cases  of 
"  cell-conductivity  "  the  transmission  of  excitation  is  much  more 
liable  to  be  disturbed,  and  is  in  a  much  higher  degree  dependent 
upon  external  and  internal  conditions,  than  within  one  and  the 
same  cell-body.     Doubtless  in  the  last  resort  this  is  the  reason  why 


170  ELECTRO-PHYSIOLOGY  chap. 

the  peristaltic  movements  of  smooth  muscular  organs,  as  we  know 
from  experiment,  are  so  easily  disturbed  and  affected  by  a  variety 
of  data.  This  applies  in  particular,  e.g.,  to  the  movements  of  the 
intestine,  which  Engelmann  treats  as  analogous  with  the  peristalsis 
of  the  ureter  (29).  Apart  from  the  richly-developed  plexuses  of 
nerves  and  ganglia  in  the  wall  of  the  intestine,  and  its  far  more 
complex  development  of  muscular  layers,  the  structure  of  the  two 
organs  shows  such  a  fundamental  agreement  that  we  are  justified 
in  assuming  a  priori  that  the  conductivity  of  excitation  and 
contingent  peristalsis  are  derived  in  both  cases  from  the  same 
principle.  In  this  connection  we  have  especially  weighty  evidence 
in  the  fact  that  a  wave  of  contraction  starting  from  any  point  in 
the  continuity  of  the  intestine  is  transmitted  under  favourable 
conditions  to  either  side  of  the  point  of  excitation,  just  as  it  is  in 
the  integument  of  the  ureter,  i.e.  peristaltically  and  anti- 
peristaltically.  This  is  not,  indeed,  the  case  invariably — nor, 
above  all,  in  every  animal.  Thus  in  the  frog's  intestine,  even 
under  the  most  favourable  conditions  of  excitability  (in 
summer  with  a  high  temperature),  local  excitation  will  scarcely 
ever  produce  anything  more  than  localised  constriction,  or  at 
most  spreading  over  a  few  millimeters.  The  reaction  is  much 
more  easily  provoked  on  the  living,  warm-blooded  intestine,  e.g., 
of  cat  or  dog,  which  has  the  further  advantage  that  on  opening 
the  abdomen  the  intestines  are  usually  quiescent,  which  is  not  to 
the  same  degree  the  case  with  the  rabbit.  But  even  here  the 
observations  required  are  not  nearly  so  certain  as  in  the  ureter. 
It  would  rather  seem  as  though  a  certain  condition  of  excitability 
in  the  intestine  was  essential  to  the  success  of  the  experiment. 
According  to  Engelmann  this  is  best  secured  when  the  animal  is 
killed  by  bleeding  from  the  large  cervical  vessels.  If  the  belly  is 
opened  soon  after  the  last  respiration,  the  intestines  are  either 
in  the  required  state,  or  pass  into  it  shortly  after.  If  the 
muscular  coat  of  a  loop  of  the  small  intestine  is  then  mechanically 
excited  at  any  point  (by  pinching  with  forceps),  Engelmann  finds 
a  vigorous  contraction  of  the  circular  layer  of  fibres,  which 
spreads  outwards  from  the  excited  spot  in  a  peristaltic  and  anti- 
peristaltic direction  over  the  whole  small  intestine,  at  a  low 
velocity  of  about  40  mm.  per  sec.  Engelmann  gets  the  same 
results  with  excitation  of  the  large  intestine.  While  at  the  first 
stimulus  the  contraction    is    pronounced  throughout    its    entire 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  171 

course,  it  exhibits  later  on  an  increasing  diminution  and  retarda- 
tion of  the  wave,  in  proportion  with  the  distance  from  the  starting- 
point,  until  finally  only  a  local  constriction  remains  visible. 

The  reaction  of  the  intestine  is  thus  in  complete  conformity 
with  that  of  the  ureter.  As  Engelmann  has  made  analogous 
observations  upon  the  stomach  and  intestine  of  rats,  mice, 
pigeons  (most  elegant),  the  oesophagus,  stomach,  and  intestine 
of  frog,  and  uterus  and  vagina  of  pregnant  rabbits,  the  conclusion 
may  be  accepted  that  in  all  cases  in  which  peristaltic  movements 
can  be  provoked,  anti-peristaltic  contraction  is  also  at  least  possible. 
It  must  be  admitted,  on  the  other  hand,  that  conductivity  of 
excitation  within  the  muscular  coat  of  the  intestine  is  frequently 
absent,  when  it  might  more  reasonably  be  expected.  This  occurs 
more  particularly  when  the  abdominal  cavity  is  opened  in  warm 
salt  solution,  when  the  intestine  usually  remains  perfectly 
quiescent.  If  under  these  approximately  normal  conditions 
any  point  is  stimulated  mechanically  by  gentle  pressure,  or 
ligature,  only  a  local,  circular  constriction  will  appear  (as 
stated  by  van  Braam  -  Honckgeest  (30)  and  confirmed  by 
Nothnagel  (31)),  which  is  confined  to  the  seat  of  excitation,  and 
never  spreads  beyond  it  in  a  peristaltic  or  anti-peristaltic  wave  of 
progression.  As  there  is  no  reason  to  suppose  that  conductivity 
is  lower  here  than  after  bleeding  the  animal,  from  Engelmann's 
point  of  view  no  other  assumption  is  possible,  but  that  the  trans- 
mission of  excitation  is  blocked  by  a  kind  of  inhibition,  possibly 
proceeding  from  the  ganglionic  plexus.  And,  experimentally,  it 
is  impossible  to  deny  the  co-operation  of  nervous  impulses, 
whether  of  an  inhibitory  or  motor  nature,  in  intestinal  peristalsis. 
The  question  then  arises  whether  the  normal  movements,  i.e.  the 
propagation  of  a  wave  of  contraction  in  one  or  the  other  direction, 
may  not  be  produced,  in  each  point  of  the  area  traversed,  by  a 
nervous  impulse.  It  can,  indeed,  hardly  be  disputed  that  such 
impulses  must  play  a  very  important  part  in  the  discharge  of  the 
contractions  which  usually  follow  in  rapid  succession.  The  extreme 
slowness  of  transmission,  which  may  be  followed  with  the  eye,  can, 
as  already  pointed  out  by  Engelmann  for  the  ureter,  be  urged 
against  the  first  view.  On  the  other  hand,  it  affords  no  better  ex- 
planation than  Engelmann's  theory  of  the  localisation  of  excitation 
effects  in  the  perfectly  normal  intestine,  or  the  sudden  extinction  of 
a  wave  of  contraction,  as,  e.^.,  often  observed  byNothnagel  {I.e.  p.  14). 


172  ELECTRO-PHYSIOLOGY  chap. 

Perhaps  the  soundest  hypothesis  is  that  propagation  of  a  peri- 
staltic wave  does  under  all  circumstances  depend  upon  muscular 
conductivity,  but  that  the  discharge  of  excitation,  as  also  the 
inhibitory  processes  which  may  become  effective  at  any  point,  are 
governed  by  the  nervous  organisation  in  the  wall  of  the  intestine. 
This  view  is  in  ultimate  agreement  with  the  striking  effects 
— observed  by  Nothnagel — in  chemical  excitation  of  the  intestine 
with  salts  of  sodium  and  potassium.  Unfortunately  it  is  not 
possible  to  test  the  hypothesis  in  question  by  putting  the 
ganglion-plexus  functionally  out  of  court  with  specific  poisons ; 
but  the  effect  of  small  doses  of  ether  and  chloroform  might  be 
investigated,  since  it  may  be  supposed  that  the  ganglion-plexus 
loses  its  excitability  earlier,  than  the  intrinsic  muscle-elements. 
The  possible  discharge  of  peristaltic  and  anti-peristaltic  waves  at 
a  certain  stage  of  death  from  hsemorrhage  may  perhaps  also 
depend  on  an  earlier  loss  of  vitality  of  the  intestinal  ganglia. 

In  conclusion,  it  may  be  said  that  conductivity  of  excitation 
in  smooth,  muscular  organs  is  rarely  obvious  and  certain ;  in  the 
majority  of  cases  it  is  wanting  altogether.  The  formation  of  an 
"  idio-muscular "  swelling  contraction  at  the  seat  of  excitation, 
which  only  disappears  very  slowly,  is  the  rule  with  localised 
excitation. 

Bibliography 


TArch.  fiir  Anat.  und  Physiol.     1860.     p.  253. 


1.  Aeby.   -"  Untersuchungen  liber  die  Fortpflanzungsgeschw.  der  Reizung  in  quer- 

I      gestr.  Muskelfasern.     Braunschweig  1863. 

2.  V.  Bezold.     Unters.  liber  die  elektr.  Erreg.  von  Muskehi  und  Nerven.     1861. 

p.  156. 

3.  Bernstein.     Unters.  iibcr  den  Erregungsvorgang  im  Nerven-  und  Muskel- 

system.     1871.     p.  79. 

4.  Hermann.    Pfliigers  Arch.     X.     1874.     p.  48. 

5.  Vee-WORN.     Psycho-physiol.  Protistenstudien.     p.  82. 

6.  Bernstein  und  Steiner.     Du  Bois  Arch.     1875.     p.  526. 

7.  RoLLET.     Pfliigers  Arch.     LII.     p.  224. 

o    o       p„      fLehrbuch  der  PhysioL     p.  26. 

I^Moleschotts  Untersuchungen.     I. 
9.  L.  Hermann.     Pfliigers  Arch.     XLV.     p.  594. 

10.  W.  KtJHNE.     Miillers  Arch.     1859.     p.  611. 

11.  A.  Pick.     Prager  med.  Wochenschrift.     1884.     No.  13. 

12.  Baierlachee.     Zeitschr.  fiir  rat.  Medicin.     1859. 

13.  Erb.     Ziemssens  Handb.  der  speciell.  PathoL  und  Therapie.     XII.     p.  242. 

14.  Chwostek.     AUgem.  Wiener  med.  Zeitung.     1883.     p.  26. 

15.  MiLRAD.     Arch,  fiir  exper.  Path,  und  Pharmakologie.     XX.     p.  217. 


II  CHANGE  OF  FORM  IN  MUSCLE  DURING  ACTIVITY  173 

16.  Ziehen  cit.  in  Franz  Friedrioh,  Ueber  das  Verhalten  der  idiomuscul.  Erreg- 

barkeit  bei  Geisteikranken.     Dissert.     Jena  1891. 
J7.  Wegener.    Arch,  fiir  mikr.  Anat.     X.     1874.     p.  293. 

18.  Laulanii?;.     Comptes  rendus.     Tom.  CI.     1885.     p.  669. 

[Denkschriften  der  mathem.-naturw.   Klasse  der  kais.  Academie  in 

19.  Rollett.    '      Wien.     LVIII. 

[Biologiscbes  Centralblatt.     XL     1891.     No.  5  und  6. 

20.  Bowman.      Philosophical  Transact.     1845. 

21.  Nasse.    Pflugers  Arch.     XVII.     p.  282. 

_„    „  f  Pflugers  Arch.     XL     1875. 

22.  Engelmann.  { _„..s        .     .       -.^.^      _„„^ 

(^  Pflugers  Arch.     LVI.     1894. 

23.  A.  FiCK.     Sitzungsber.  der  phys. -med.  Ges.  zu  Wiirzburg.     1874.    Sitzung  vom 

13.  Juni. 

24.  BlEDERMANN.     Beitrage  zur  allgem.  Muskel-  und  Nervenphysiologie.     XXII. 

p.  101.     (Wiener  academ.  Sitzungsber.     Bd.  97.     Abth.  III.     1888-89.) 

25.  Engelmann.    Pfliigers  Arch.     IV.     p.  44. 

26.  Du  Bois-Reymond.    Arch,  flir  Pliysiologie.     1890. 

27.  Romanes.     Philosoph.  Transact.    1866,  1867,  1876  und  1877.     (Abhandlungen 

liber  Medusen. ) 

28.  Th.  W.  Engelmann.     Pfliigers  Arch.     11.     1869.     p.  243. 
29. Pflugers  Arch.     IV.     p.  33. 

30.  Van  Braam-Honckgeest.    Pflugers  Arch.     VI. 

31.  NoTHNAGEL.     Beitrjige  zur  Physiol,  und  Pathol,  des  Darmes.     1884.     p.  15. 


CHAPTEE    III 

ELECTKICAL    EXCITATION    OF    MUSCLE 

The  electrical  current  undoubtedly  ranks  first  among  all  the 
artificial  stimuli  of  irritable  substances  at  our  command.  And 
this  not  merely  on  account  of  its  easy  application,  and  the  pos- 
sibility of  measuring  its  intensity  by  the  finest  gradations,  but 
above  all  in  regard  to  the  specific  nature  of  its  action. 

Whenever  the  electrical  current  has  been  referred  to  as  an  ex- 
citation in  the  preceding  observations,  it  signified  almost  exclusively 
single,  or  rapidly  repeated,  induction  shocks,  the  primary  object 
being  to  produce  a  momentary  stimulus,  easily  varied  in  strength, 
which  should  injure  the  excitable  portions  as  little  as  possible. 
But,  on  the  other  hand,  the  more  exact  investigation  of  the  mani- 
festations of  excitation  produced  by  the  constant  mirrent  in  muscle 
is  of  great  interest,  and  of  the  highest  importance  in  estimating 
the  mode  of  action  of  the  electrical  current.  As  regards  the 
technique  of  the  experiments,  some  preliminary  observations  on 
method  are  advisable.  In  all  the  earlier  experiments  on  animal 
tissues  in  which  the  electrical  current  served  as  a  means  of  excita- 
tion, the  excitable  parts  were  stretched  over  convenient  metal 
electrodes,  usually  made  of  platinum,  by  means  of  which  the 
current  was  led  into  them.  The  value  of  this  method  was,  how- 
ever, much  diminished  by  the  polarisation  current  invariably 
associated  with  it,  so  that  it  became  a  sine  qud  non  under  all 
conditions,  to  employ  non-polarisable  electrodes  whenever  constant 
currents  were  made  use  of — still  more  so  with  strong  currents  and 
prolonged  closure.  Ever  since  du  Bois-Eeymond  enlarged  the 
technique  of  electro-physiology  by  the  invention  of  his  unpolaris- 
able  combination  of  amalgamated  zinc  and  zinc  sulphate,  in  order 
to  lead  off  currents  of  animal  electricity,  these  electrodes  have 


ELECTRICAL  EXCITATION  OF  MUSCLE 


175 


found  the  widest  application  in  excitation  experiments,  several 
different  forms  having  been  adopted.  When  it  is  required  to 
lead  a  current  into  a  striated  muscle,  the  shifting  of  the  contract- 
ing muscle  under  the  electrodes  in  contact  with  it  is  a  ready- 
source  of  fallacy,  which  can  only  be  avoided  where  the  electrodes 
are  fixed  to  the  muscle,  or  bones  into  which  it  is  inserted,  so 
as  to  follow  every  movement.  Hering  was  the  first  to  construct 
non-polarisable,  shifting  electrodes  for  the  frog's  sartorius,  which, 
from  its  regular  structure  of  parallel  fibres,  is  singularly 
appropriate  to  such  experiments,  and  is  easily  prepared  without 
disturbing  its  natural  relations  with  the  bones  of  the  leg  and  pelvis  : 


Fig.  71. — Apparatus  for  investigating  tlie  polar  effects  of  the  electrical  current  in  muscle 
(double  myograph).     A  non-polarisable  movable  electrode.     (Hering.) 

these  electrodes  serve  for  a  variety  of  purposes  (1).  "A  5-5  cm. 
glass  tube  (Fig.  71)  is  provided  at  the  upper  end  with  a  split 
brass  holder,  carrying  two  diametrically  opposite  points,  which  fit 
into  the  holes  of  a  pivot,  so  that  the  vertically  dependent  tube  may 
easily  turn  on  the  points,  and  oscillate  from  them.  The  pivot  is 
fixed  to  a  brass  ring  {m),  which  can  be  moved  along  a  horizontal 
rod  {q)  of  bone  or  ebonite.  A  short  ebonite  cylinder  (Ji)  is  pushed 
over  the  lower  end  of  the  glass  tube,  the  opening  of  which  is  the 
continuation  of  the  bore  of  the  tube,  and  is  transversely  pierced 
in  such  a  way  that  a  slender  bone  like  the  tibia  or  os  ileum  of  the 
frog  can  be  passed  through  the  hole,  and  fixed  by  a  screw.  A 
small  amalgamated  zinc  rod  is  dropped  into  the  tube  from  above. 


176  ELECTRO-PHYSIOLOGY  chap. 

and  supported  by  a  brass  stirrup  fixed  to  its  upper  end,  which  again 
is  attached  to  the  brass  holder  of  the  tube.  This  stirrup  is  con- 
tinued on  the  other  side  as  a  short,  copper  wire  bent  downwards 
to  dip  into  a  steel  cup  filled  with  mercury  (s).  As  the  rod  swings 
to  and  fro,  contact  is  made  between  the  end  of  the  wire  and  the 
mercury.  At  the  lower  end  of  the  pool  is  a  terminal  to  which 
the  wire  is  fixed.  When  in  use,  the  ebonite  collar  and  bottom  of 
the  glass  tube  are  filled  with  salt  clay,  the  upper  part  with  solu- 
tion of  zinc  sulphate,  with  the  zinc  rod  dipping  into  it.  After 
the  bone  has  been  pushed  through  the  orifice  of  the  ebonite  collar 
into  the  clay,  it  is  fixed  by  the  screw.  The  bone  at  the  other  end 
of  the  muscle  is  similarly  fixed,  so  that  the  muscle  is  now 
horizontally  stretched  between  the  two  electrodes.  Further,  a 
thread  is  attached  to  the  lower  part  of  each  electrode,  connecting 
it  with  a  muscle  pointer.  Either  of  the  electrodes  can  be  fixed, 
leaving  the  other  to  follow  the  shortening  of  the  muscle." 

Assuming  that  the  electrode  of  the  pelvic  bone  is  fixed,  the 
movement,  or  change  of  form,  of  the  whole  muscle  can  easily 
be  observed  and  graphically  recorded,  if  the  other  free  electrode 
is  connected  with  a  long  pointer  (s),  by  a  thread  running 
horizontally  over  two  pulleys  (E  and  r,  Fig.  71)  with  a  weight 
at  the  end  of  it,  the  pointer  again  being  attached  to  the  axis  of 
the  larger  pulley.  Since  the  writing-point  naturally  describes  an 
arc  of  a  circle,  the  curve  of  contraction  on  the  smoked  surface  is 
more  or  less  distorted,  which,  however,  matters  little  in  the  present 
consideration.  If  under  these  conditions  the  effect  of  varying 
strengths  of  the  constant  current  is  investigated  upon  a  curarised 
(denervated)  sartorius,  it  is  easy  to  see  that  under  the  most 
favourable  conditions  of  excitability  in  the  muscle,  permanent 
closure  of  a  weak  current  never  provokes  more  than  a  single 
brief  "twitch,"  which  is  at  first  insignificant  in  height,  but 
rapidly  attains  its  maximal  value,  if  the  current  increases  in 
intensity. 

Beyond  a  certain  limit  of  intensity  the  height  of  the  make 
twitch  remains  constant  ;  other  changes,  however,  appear  in 
the  curve  to  which  we  shall  refer  later.  On  comparing  the 
maximal  twitches  produced  by  single  induction  shocks  with  the 
maximal  "  make  twitches  "  of  the  constant  current  under  uniform 
conditions,  we  are  at  once  struck  by  the  much  greater  height,  as 
well   as    the   blunt,  rounded   top,  of  the   latter.      This    can   be 


ELECTRICAL  EXCITATION  OF  MUSCLE 


17; 


detected  ev-en  at  a  slow  rate  of  the  recording  surface,  but  is 
much  plainer  with  a  quick  movement.  According  to  Tigerstedt 
(2)  the  process  of  each  make  contraction  must  be  of  a  tetanic 
character,  since  the  corresponding  curves  are  much  more  ex- 
tended than  in  twitches  provoked  by  induction  currents  (Fig. 
72),  But  it  is  needless  to  say  that  there  is  not  necessarily 
any  true  "  tetanus,"  i:e.  contraction  resulting  from  summation. 
From  these  facts  alone  we  may  conclude  that  besides  the  intensity 
of  current,  its  duration  in  the  muscle  also  affects  the  strength 
of  excitation  (or  contraction),  while  this  appears  yet  more 
plainly   from    corresponding    experiments    on   sluggish    muscles, 


Fig.  72. — 1-8,  Contraction  curves  on  excitation  of  the  muscle  by  single  indiTction  .shocks  ;  9-19,  con- 
traction curves  (make  twitches)  on  exciting  with  the  constant  current  ("  tetanus  "  character). 
(Tigerstedt.) 

where  the  magnitude  of  effect  as  dependent  upon  the  duration  of 
the  excitation  appears  to  be  in  exact  inverse  ratio  with  the 
mobility  of  the  particles  of  an  irritable  substance.  The  extra- 
ordinarily small  and  often  negative  effect  of  single  induction 
shocks  on  many  protozoa,  and  on  vegetable  protoplasm,  is  well 
known,  while  in  smooth  muscle  such  short  stimuli,  if  they  act 
at  all,  first  take  effect  at  a  high  intensity,  although  they  seldom 
or  never  fail  to  excite  the  rapidly  twitching  striated  fibres. 
This  is  remarkably  well  seen  on  every  relaxed  (a-tonic)  pre- 
paration from  the  adductor  muscles  of  anodonta  (3).  From 
these,  as  was  said  above,  it  is  easy  to  obtain  a  preparation  as 
susceptible  to  electrical  excitation  as  the  frog's  sartorius  (Fig.  73). 

N 


178 


ELECTRO-PHYSIOLOGY 


Then,  after  permanently  fixing  one  half  of  the  shell,  non- 
polarisable  brush  electrodes  can  be  applied  on  both  sides,  as  near 
as  possible  to  the  insertion  of  the  muscular  band  (which  usually 
consists  of  parallel  fibres),  while,  in  order  to  prevent  any  shifting 
of  the  electrode  corresponding  with  the  other  movable  half  of  the 
shell,  the  current  at  this  point  is  best  led  in  by  a  short  loop  of 
thread. 

If  a  current  of  adequate  strength  is  then  sent  through  the 
relaxed  muscle,  changes  of  form  may  be  observed  which,  apart 
from  the  sluggishness  of  reaction  more  or  less  characteristic  of 
all  smooth  muscle,  concur  on  the  whole  with  those  exhibited  by 
striated  muscle   under   analogous    conditions.      As   regards  form 

and  process  of  contraction  during 
closure  of  the  current,  the  resulting 
curve  will  of  course  rarely  corre- 
spond with  the  process  designated  in 
re  the  time-distribution  of  the  contrac- 
tions of  striated  muscle,  the  "  make 
twitch."  Apart  from  the  slowness 
with  which  the  whole  process  occurs, 
the  difference  of  duration  between 
the  contraction  and  relaxation  phases 
(periods  of  rising  and  falling  energy) 
is  much  more  marked  in  smooth 
molluscan  muscle,  which  gives  a  dis- 
tinct and  peculiar  character  to  its 
curve  of  contraction.  Two  cases 
must  here  be  distinguished,  that  in  which  the  current  is  opened 
before,  or  as  soon  as,  the  muscle  has  reached  its  maximum  of 
shortening,  and  that  in  which  there  is  a  long  period  of  closure. 
In  the  first  case,  at  least  under  certain  conditions,  e.g.  with 
warmed  and  therefore  quickly  reacting  preparations,  curves  are 
obtained,  which  from  their  form  and  process  might  be  regarded  as 
extended  twitch  curves,  since  not  only  does  the  shortening  rapidly 
rise  to  a  considerable  height,  but  the  relaxation  also  occupies  a 
comparatively  short  time  (Fig.  74). 

In  other  cases  a  longer  closure  of  the  circuit  produces 
curves  which  rise  abruptly  at  the  moment  of  closure,  without 
sinking  down  again,  corresponding  with  a  persistent  and  uniform 
shortening  of  the  muscle.      Under  these  conditions  the  closure 


Fig.  73. — Schema  of  electrical  excitation 
in  adductor  muscle  of  molluscs. 


ELECTRICAL  EXCITATION;  OF  MUSCLE 


179 


may  last  a  minute,  and  the  muscle  remain  nearly  as  long  in  a 
state  of  maximal  shortening, — when  excited  by  weak  as  well 
as  by  strong  currents.      The  dependence  of  contraction   magni- 


Fig.  74. — Closure  contraction  of  adductor  muscle  of  Auodonta  (excitation  by  the  constant 
current) ;  (s),  closure  ;  (o),  opening. 

tude  on  duration  of  closure  is  most  plainly  seen  on  the  prepara- 
tion in  question  if  the  circuit  is  opened  hefore  the  maximum  of 
shortening  is  reached.  Constant  currents  which  produce  maximal 
contraction  of  the  muscle  when  closed  for  3—4  sees,  often  effect 
a  merely  insignificant  shortening  if  closed  for  only  ^  sec.  At 
this    ranRe   the    closure    contraction    is    greater   with    unaltered 


Fic;.  75. — Effect  of  duration  of  current  on  contraction  magnitude  of  adductor  muscle  of  Anodonta 
(excitation  with  constant  current) ;  («),  duration  of  closure=j  sec.  ;  (&),  =  !  sec.  ;  (c),  =4  sees. ; 
(o),  opening  contraction.     (Biedermann.) 

strength  of  current  in  proportion  with  the  time  during  which  cur- 
rent passes  (Fig.  75).  This  agrees  with  the  fact  that  single  induc- 
tion shocks  only  stimulate  the  most  excitable  preparations  at  a 
very  high  intensity,  so  far  as  may  be  concluded  from  the  visible 


180 


ELECTRO-PHYSIOLOGY 


changes  of  form  (Fig.  76).  Fresh  muscles,  or  those  which,  though 
older,  are  still  in  a  state  of  considerable  tonic  contraction, 
generally  appear  quite  insensible  to  induced  currents. 

The  advantages  of  a  sustained  passage  of  current  over  brief 
"  current  impacts  "  is  also  seen  in  tetanising  excitation  'periodically 
repeated.  Fick  pointed  out  that  the  rapid  make  and  break, 
by  hand,  of  an  intrinsically  effective  constant  current,  generally 
failed  to  excite  smooth  molluscan  muscle— yet  the  duration  of 
the  single  impacts  here  is  considerable ;  if  it  is  still  further 
lessened,  stronger  and  stronger  currents  will  be  required  to  pro- 
duce any  excitation.  This  is  especially  striking  in  excitation 
with  a  rapid  succession  of  induced  alternating  currents,  and  Fick 
states  "  that  in  the  same  circuit  that  closes  the  secondary  coil  of 
an  ordinary  induction  apparatus,  a  frog's  muscle  may  fall  into 
the  most  lively  tetanus,  while  the  molluscan  muscle  shows 
no  sign  of  excitation,"  and  that  this  even  occurs  with  currents 


jLa_jlj_jl1j 


Fig.  76. — Contraction  curves  of  adductor  muscle  of  Anodonta,  excited  by  single  make  and  break 
induction  curreiits  (s  and  o)  of  increasing  strength  (a,  at  greatest  distance  of  coil). 

that  are  strong  enough  to  throw  the  muscles  of  the  experimenter's 
hand  into  tetanus  (4). 

Engelmann's  observations  on  the  ureter  (5)  naturally  fall 
into  line  with  these  experiments  on  the  smooth  adductor  muscle 
of  molluscs.  Here,  too,  it  is  easy  to  demonstrate  that  the  make 
contraction  occurs  only  when  the  duration  of  current  exceeds  a 
certain  limit,  which  is  lower  in  proportion  with  the  strength  of  the 
current.     This  is  plain  from  the  accompanying  table  (Engelmann). 


strength  of  current  in  rheochord 

Minimum  closure, 

required  to  produce 

resistance. 

contraction. 

4000 

cm. 

<4 

quarter  second. 

500 

\ 

50 

1 

25 

2 

15 

3 

12 

4 

11 

5 

10-5 

6 

HI  ELECTRICAL  EXCITATION  OF  MUSCLE  181 

In  conformity  with  this,  "  powerful  intensities  "  of  current  are 
required  to  produce  contraction  of  the  ureter  by  single  in- 
duction currents.  Engelmann  was  the  first  to  accomplish  this  by 
taking  metallic  electrodes  (2dnc  wires),  shortening  the  intra- 
polar  tract,  and  connecting  the  primary  coil  of  du  Bois'  induction 
apparatus  with  2—4  Grove  cells. 

We  have  repeatedly  stated  that  effects  which  can  only  be 
determined  in  voluntary  muscle  by  complicated  methods  and 
the  finest  instruments,  can  be  observed  directly  in  smooth 
muscle.  This  also  applies  in  a  marked  degree  to  the 
effect  of  duration  of  current  upon  excitation.  It  was  shown 
above  that  the  marked  difference  in  the  height  of  maximum 
twitches,  according  as  excitation  is  with  the  induced  or  the 
constant  current,  is  a  sign  that  duration  of  current  is  in  the 
last  case  an  intrinsic  factor.  Tick  was  the  first  to  establish  exact 
data  re  constant  currents  of  uniform  intensity  and  varying  dura- 
tion, for  striated  frog's  muscle.  This  is  much  harder  than  in 
smooth  muscle,  since,  as  might  be  presumed,  the  time  during 
which  current  must  pass  in  order  to  produce  a  true  excitation  is 
much  shorter  in  striated  muscle.  And  in  fact  in  experiments 
where  closure  has  been  effected  by  means  of  an  ordinary  key, 
there  is  never  any  perceptible  effect  of  duration  of  current  on 
the  height  (magnitude)  of  the  twitch  at  closure,  as  may  be 
readily  understood.  If  current  once  lasts  long  enough  for  the 
muscle  to  reach  its  maximum  of  contraction,  the  closure  twitch 
cannot  be  affected  by  any  further  duration.  And  this  must  more 
especially  be  the  case  when  the  circuit  is  opened  and  closed, 
however  quickly,  by  the  hand  of  the  operator. 

Under  certain  conditions  striated  skeletal  muscle  also  becomes 
modified,  so  that  the  relative  inefficacy  of  very  short  stimuli  is  ex- 
hibited, without  any  particular  refinement  of  instruments.  Briicke 
found  that  the  sensibility  of  striated  muscle  to  short  currents 
diminished  when  it  was  curarised.  It  has  long  been  known  in 
clinical  medicine  that  paralysed  striated  muscles  exhibit  a  certain 
inability  to  react  to  short,  induced  currents,  although  their 
relation  to  variations  of  the  constant  current  is  perfectly  normal, 
and  this  has  been  the  basis  of  a  great  number  of  investigations 
(6).  Erb  {I.e.),  for  instance,  found  in  paralysis,  such  as  Bell's 
palsy  in  rheumatism,  or  by  section  of  the  nerve,  that  the 
sensibility  of  the  muscle  to   short  currents  was  diminished,  or 


182  ELECTRO-PHYSIOLOGY 


completely  abolished,  while  it  was  fully  maintained  and  even 
heightened  for  the  constant  current.  Neumann  observed  similar 
chanoes  in  fatio-ued  or  moribund  conditions. 

Along  with  these  changes  there  is  the  gradual  development 
of  a  much  more  sluggish  process  of  contraction,  so  that  here  too 
contractile  substances  with  a  slow  reaction  require  a  longer 
period  of  excitation  than  those  which  react  quickly.  This  is 
developed  to  such  an  extreme  degree  in  many  smooth  muscles, 
that  one  is  justified  in  saying  that  moribund  striated  muscle, 
especially  at  the  beginning  of  degeneration,  approximates  to  a 
certain  extent,  in  its  physiological  properties,  to  smooth  muscle. 
The  differences  described  are  most  marked  in  a  series  of  observa- 
tions (not  yet  published),  by  T.  Krehl  (Jena),  on  frogs,  in  which 
one  sciatic  nerve  had  been  divided  at  the  thigh.  After  |-  year 
the  comparison  of  the  two  gastrocnemii  still  exhibited  marked 
differences  on  excitation  with  tetanising,  or  single,  induction  cur- 
rents, or,  on  the  other  hand,  with  the  constant  current.  In  the 
first  case  the  coil  had  almost  to  be  pushed  home  before  the 
slightest  effect  could  be  produced  in  the  paralysed  muscle ;  in 
the  second  an  excessively  marked,  persistent  contraction  was 
exhibited  during  closure.  The  muscle  of  the  uninjured  side 
reacted  normally. 

A.  Fick  (7)  was  the  first  to  show  by  unexceptionable  experi- 
ments, that  the  make  excitation  is  a  function  of  duration  of  current 
in  this  case  also.  In  order  to  regulate  the  duration  of  a  single 
"  impact  of  current  "  as  required,  Tick  used  a  spring-contact,  which 
conducted  a  metal  point  rapidly  over  a  metallic  plate  of  varying 
breadth  (spiral  rheotome).  From  this  it  appeared  that,  with  excita- 
tion of  a  normal  striated  frog's  muscle,  the  magnitude  (height)  of 
twitch  produced  by  closure  of  the  constant  current  depended 
not  merely  on  strength  of  current,  but  on  the  time  during 
which,  at  constant  density,  it  was  passing  through  the  muscle. 
The  limit  below  which  the  duration  of  closure  must  not  fall, 
if  the  height  of  twitch  is  to  remain  maximal,  corresponds 
according  to  Fick  with  about  O'OOl  sec.  Even  if  this  value 
is  only  approximate  it  shows  that  the  difference  between  the 
duration  of  closure  required  to  produce  an  effective  make 
excitation  in  smooth  muscle,  and  in  striated  frog's  muscle,  is 
enormous.  We  shall  see  later  that  a  similarly  graduated  differ- 
ence also  occurs  between  striated  muscle  and  medullated  nerve, 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  183 

a  still  shorter  duration  of  closure  being  sufficient  to  excite  the 
latter. 

Summing  up  the  results  of  the  preceding  observations,  we 
may  say  that  under  all  conditions  a  current  of  given  strength 
must  traverse  the  muscle  for  a  perceptible  time,  in  order  to 
bring  it  from  a  state  of  rest  into  that  of  maximal  excitation, 
corresponding  with  the  intensity  of  the  same  current.  If  the 
cause  of  excitation,  i.e.  the  current,  acts  for  too  short  a  time,  a 
weak  contraction  only  will  ensue,  because  the  new  state  cannot 
develop  itself  fully ;  with  still  shorter  duration  of  current,  the 
effect  is  altogether  wanting,  because  the  stimulus  does  not  act 
long  enough  to  induce  in  any  perceptible  degree  those  changes 
in  the  muscular  substance  which  are  the  fundamental  cause  of 
contraction.  The  time  required  varies  within  a  very  wide  range 
in  different  muscles  with  quick  reaction,  but  is,  generally  speaking, 
greater,  as  the  period  of  contraction  is  more  sluggish. 

If  we  may  conclude  from  the  above  that  the  excitatory 
process  is  caused  by  the  current,  not  merely  at  the  moment  of 
its  commencement,  but  also  during  its  ]passage,  this  is  still  more 
certain  from  a  closer  investigation  of  the  changes  of  form  in  a 
muscle  during  ijersistent  closure  of  current.  We  have  already 
pointed  out  in  smooth  molluscan  muscle  that  it  may,  under  these 
conditions,  remain  as  long  as  a  minute  in  unbroken,  persistent 
contraction.  The  magnitude  of  this  "  persistent  closure  con- 
traction "  increases  up  to  a  certain  limit  with  the  strength  of  the 
exciting  current,  but  the  effect  per  se  is  quite  evident  at  all 
working  grades  of  intensity ;  indeed,  it  may  be  said  that  the 
persistent  closure  contraction  is,  generally  speaking,  the  single 
form  of  contraction  in  smooth  molluscan  muscle  that  corresponds 
with  persistent  closure.  If  the  reaction  of  striated  muscle  is 
compared  under  the  same  conditions,  there  are  noticeable  differ- 
ences. We  have  already  found  that  below  a  certain  limit  of 
current  intensity  a  single  "  twitch  "  is  alone  provoked  at  closure, 
the  muscle  shortening  rapidly,  and  elongating  again  almost  as 
quickly,  even  when  the  circuit  remains  closed.  When  in  any 
given  case  the  closure  twitch  has  reached  its  maximum,  a  further 
increase  of  current  intensity  produces  no  increment  in  height  of 
contraction,  but  there  are  certain  changes  in  the  form  of  the 
contraction  curve,  which  express  the  persistent  shrinking  of  the 
muscle  during  the  entire  passage  of  the  current. 


184  ELECTRO-PHYSIOLOGY  chap. 

Wundt  (8)  was  the  first  to  observe  that  the  muscle  does 
not  recover  its  normal  length  immediately  after  the  closure  twitch 
has  subsided,  but  exhibits  a  greater  or  less  degree  of  shortening, 
which  only  relaxes  suddenly  and  sharply  when  the  circuit  is 
opened,  provided  this  break  does  not  in  itself  excite  the  muscle 
and  produce  a  vigorous  second  contraction  (opening  twitch).  The 
magnitude  of  the  persistent  closure  contraction  increases  in  this 
case  also,  up  to  a  certain  point,  with  the  strength  of  the  exciting- 
current  ;  it  is — at  any  rate  under  the  given  conditions — (re- 
cording the  changes  of  form  with  Bering's  double  myograph)  im- 
perceptible with  weak  currents,  but  expresses  itself  plainly  later 
on  in  a  specific  section  of  the  curve,  inasmuch  as  the  descending 
shoulder  of  the  curve  does  not  reach  the  abscissa,  but  runs  along 
more  or  less  above  it,  so  long  as  the  current  remains  closed 
(Fig.  77,  Z). 


Fig.  77.— Sartoi-ius  fixed  in  tlie  middle  (double  myograph).    Successive  excitations  at  closure  with 
uniform  strength  and  direction  of  current.    Effect  of  (local)  fatigue  at  the  kathode. 

With  the  application  of  very  strong  currents,  the  make 
twitch  eventually  appears  only  like  a  hook,  since  the  muscle 
relaxes  very  little  after  reaching  its  maximum  of  shortening, 
thus  approximating  to  the  normal  reaction  of  smooth  molluscan 
muscle.  This  seems  to  appear  earlier,  and  to  be  more  marked, 
in  preparations  that  are  already  fatigued,  and  less  capable  of 
reacting.  The  persistent  closure  contraction  is  in  general  capable 
of  much  greater  resistance  than  the  closure  twitch,  as  appears 
inter  alia  from  the  fact  that  when  a  muscle  is  fatigued  by 
repeated  closure  with  unaltered  direction  of  current,  the  initial 
twitch  rapidly  diminishes  in  size,  and  at  last  ceases  to  appear 
altogether,  while  the  persistent  contraction  decreases  only  very 
slowly  with  progressive  fatigue  of  the  muscle.  The  initial 
twitch  has  long  disappeared,  when  each  new  closure  still  excites 
the  muscle  to  persistent  shortening  in  almost  the  same  degree 
as   at   the  beginning  of  the  experiment  (Fig.  77,  K);  it  is  not 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  185 

till  much  later  that  this  effect  also  vanishes.  In  every  such 
case  striated  muscle  then  reacts  from  the  beginning  exactly 
like  smooth  moUuscan  muscle ;  there  is,  as  a  rule,  no  twitch  at 
closure,  only  a  more  or  less  considerable  sustained  contraction, 
so  that  in  this  particular  also  there  is  agreement  between 
fatigued  striated  and  normal  smooth  muscle.  Taken  in  con- 
junction with  previous  evidence,  the  persistent  closure  contraction 
shows  indisputably  that  the  electrical  current  sets  V2)  a  'process  of 
excitation  in  striated,  as  in  smooth,  muscle,  throughout  the  duration 
of  its  'passage. 

The  effect  of  duration  of  current  is  even  more  striking  in  the 
opening  excitation  than  at  closure,  so  that  the  influence  of  cur- 
rent intensity  is  relatively  at  a  discount.  With  low  current 
intensity,  and  short  duration  of  closure,  there  will  be  no  opening 
excitation ;  currents  to  the  closure  of  which  a  curarised  muscle 
responds  with  maximal  twitches  and  strong  sustained  contraction, 
often  provoke  no  trace  of  visible  excitation  when  they  are  broken, 
or  in  the  most  favourable  cases  a  weak  opening  twitch  may 
occur  after  prolonged  closure  only.  Although,  on  the  other  hand, 
strong  currents  will  often  effect  an  obvious  break  excitation 
after  even  a  short  closure,  it  is  not  primarily  the  intensity  of  the 
current  which  causes  the  break  effect,  but  the  duration  of  its 
passage.  The  same  alterations  as  may  be  observed  in  the  curve  of 
the  closure  contraction  with  increasing  intensity  of  current,  appear 
again  in  the  curve  of  the  opening  contraction,  if  the  passage  of 
current  which  precedes  it  has  been  of  long  enough  duration  (24). 

The  simplest  change  of  form  with  which  a  striated  muscle 
reacts  to  the  opening  excitation  is  again  a  (break)  tioitch;  contrac- 
tion occurs  quickly  at  the  moment  the  circuit  is  opened,  and  the 
muscle  almost  as  quickly  returns  to  its  normal  resting  pro- 
portions, so  that  curves  are  produced  analogous  to  those  of  the 
closure  of  weaker  currents.  But  the  opening  twitch  only  occurs 
in  this  simple  form  when  the  muscle  is  highly  excitable,  the 
current  not  too  strong,  and  the  duration  of  closure  not  unduly 
lengthened.  Strong  currents  almost  regularly  produce  more  or 
less  extended  (tetanic)  opening  twitches,  which  always  appear  to 
be  antagonistic  to  the  previous  persistent  closure  contraction, 
since  the  ascending  shoulder  of  the  curve  rises  from  the  line 
of  the  persistent  contraction  as  its  abscissa,  while  the  descending 
portion  drops  to  the  original  abscissa  line  (Fig.  78). 


186  ELECTRO-PHYSIOLOGY 


If  a  strong  current  is  kept  closed  until  every  trace  of 
persistent  shortening  has  vanished,  the  muscle  will  not  resume 
its  natural  length  directly  the  break  twitch  has  expired,  but 
remains  iMrsisUntly  shortened  ("  persistent  opening  contraction  ") ; 
the  closure  of  a  homodromous  current  in  this  case  produces 
not  a  shortening,  but  an  elongation  of  the  muscle ;  it  is  easy 
to  show  that  not  merely  the  height  of  the  opening  twitch, 
but  the  magnitude  of  the  persistent  opening  contraction  also, 
increase  up  to  a  certain  limit  with  the  duration  of  the  previous 
passage  of  current.  The  twitch  entirely  fails  to  appear,  both  at 
closure  and  opening,  with  diminished  excitability  of  the  muscle, 
and  only  the  persistent  contraction  marks  the  effects  of  excita- 
tion. The  muscle  then  shortens  when  the  current  is  opened, 
remains  contracted  for  some  time,  and  lengthens  instantaneously 


Fig.  78.— Series  of  curves  of  twitches  from  the  sartorius,  fixed  by  its  belly,  in  the  double  myograph.  A', 
Katliodic  ;  A,  anodic  half.  The  figures  correspond  with  the  rheochord  resistance.  Effect  of 
increasing  strength  of  cui-rent  (s,  closure  ;  o,  opening). 

upon  closure  of  the  homodromous  current.  Thus,  as  regards 
striated  muscle,  three  chief  forms  of  contraction  may  be  dis- 
tinguished at  the  opening  as  at  the  closing  excitation :  (i)  the 
simple  twitch,  (ii)  twitch  immediately  followed  by  persistent 
shortening,  (iii)  persistent  contraction  without  previous  twitch. 
Of  these,  (i)  corresponds  with  the  weakest  degree  of  excitation, 
(iii)  is  a  fatigue  effect.  It  is  evident  that  Wundt  studied  only 
the  third  form  in  his  experiments  on  the  opening  excitation ;  i.e. 
he  says  :  "  If  the  circuit  is  closed  for  a  long  period,  contraction 
will  follow  upon  breaking  it ;  this  occurs  much  more  slowly  than 
contraction  in  a  twitch ;  it  remains  some  time  at  its  maximum, 
and  only  gradually  gives  way  to  elongation  "  (8,  p.  142).  Against 
this  it  must  be  observed  that  eveu  when  the  current  has  been 
passing  for  hours,  a  definite  twitch  will  follow  on  breaking  it, 
provided  that  excitability  and  conductivity  are  preserved  as  far 
as  possible. 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  187 

Since  the  sluggish,  smooth  muscles  do  not  yield  any  twitch, 
it  is  self-evident  that  at  break,  as  at  make,  of  a  constant  current, 
the  change  of  form  will  always  correspond  in  character  with 
the  more  or  less  pronounced  persistent  contraction  only.  If 
experiments  are  tried  with  the  adductor  muscle  of  anodonta, 
when  free  of  tonus,  and  as  relaxed  as  possible,  somewhat  strong 
currents,  and  a  long  closure,  will  be  required  to  produce  a  distinct 
opening  contraction,  the  curve  of  which  then  appears  superposed 
upon  the  curve  of  the  closure  contraction — near  its  summit 
— in  consequence  of  the  slow  relaxation  of  the  muscle  (Fig. 
75,  o).  On  the  ureter  of  the  rabbit  also,  Engelmann  ascertained 
that  in  order  to  produce  a  break  contraction,  the  closure  must 
exceed  a  certain  duration.  It  is  arrived  at  earlier  with  strong 
than  with  weak  currents,  in  proportion  with  the  increase  of 
excitability.  "  With  greater  strength  of  current,  and  higher 
excitability,  an  opening  contraction  may  occur  even  after  a 
closure  of  less  than  ^  sec. ;  with  currents  of  lower  inten- 
sity, and  with  diminished  excitability,  a  closure  of  30  —  60 
sees,  is  not  seldom  required."  For  the  rest — given  the  same 
current,  and  a  certain  degree  of  excitability — the  total  duration 
of  the  break  contraction  increases  up  to  a  certain  limit,  with 
increasing  duration  of  closure.  Accordingly,  both  on  opening  and 
on  closing  the  constant  current,  a  jJ^i'sistent  excitation  will  be 
produced,  not  merely  in  smooth  muscle,  but  in  striated  muscle 
also,  the  magnitude  of  which  depends,  in  the  first  case,  mainly  on 
current  intensity,  while  in  the  second  it  is  also  to  a  considerable 
degree  dependent  upon  the  duration  of  passage  of  the  current. 

The  reaction  of  smooth  molluscan  muscle  that  has  shortened 
at  a  certain  degree  of  tonus,  is  quite  characteristic  with  regard  to 
the  appearance  of  the  break  excitation.  We  have  already  seen 
that  in  each  such  case  the  closure  of  a  battery  current,  if  effective  at 
all,  produces  only  a  very  weak  excitation.  As  the  break  stimulus, 
both  in  striated  and  in  smooth  muscle  (free  of  tonus),  always 
produces  a  much  smaller  effect  than  the  make  stimulus  under 
the  same  conditions,  it  is  very  striking  that  the  first  visible 
effect  of  excitation  upon  a  fresh,  highly  "  tonic,"  preparation  of 
molluscan  muscle  should  occur  without  exception  on  opening  the 
circuit  only,  while  its  closure  either  produces  no  effect,  or  a 
shortening  that  is  minimal  in  comparison  with  the  opening  con- 
traction (Fig.  79,  a).     Even  when  the  intensity  of  a  just  effective 


ELECTRO-PHYSIOLOGY 


current  is  considerably  increased  in  the  sequel,  no  essential 
change  can  be  observed  in  the  response  of  the  muscle,  unless  it 
be  that  the  opening  contraction  then  appears  vigorously  after  only 
a  short  duration  of  closure.  With  any  effective  intensity  of 
current  a  period  of  1-2  sees,  is  usually  sufficient  to  cause 
perceptible  shortening  of  the  muscle;  but  the  effect  increases 
within  certain  limits,  if  the  closure  is  lengthened  with  un- 
altered direction  and  intensity  of  current.  It  is  to  be  noticed 
that  the  magnitude  of  the  break  contraction  diminishes  very 
rapidly  with  repeated  excitation  of  the  same  preparation;  this 
seems  to  coincide  with  the  extremely  slow  subsidence  of  all 
excitation  phenomena,  and  thus  of  the  persistent  opening  con- 


PiG.  79.— Contraction  curve  of  adductor  muscle  of  Anodonta  on  excitation  with  the  constant  cur- 
rent, a,  Immediately  after  preparation  (pronounced  tonus) ;  b,  4  hours  later,  after  relaxa- 
tion of  the  muscle  ;  (s),  closure  ;  (o),  opening  of  current. 

traction  also,  since  it  is  minutes  before,  at  uniform  loading, 
the  shortened  muscle  resumes  its  original  proportions.  Under 
these  conditions  it  is  obvious  that  only  in  a  very  limited  sense 
can  there  be  any  comparison  of  the  results  of  repeated  excitation 
of  one  and  the  same  muscle  under  rapidly  alternating  experi- 
mental conditions  {e.g.  differences  of  closure  and  current  inten- 
sity), since  from  the  extreme  slowness  of  relaxation  the  first 
experiment  alone  can,  as  a  rule,  be  taken  into  consideration. 
We  may  assume  that  other  smooth  muscles  with  a  developed 
"  tonus  "  will  react  in  the  same  way  towards  galvanic  currents  as 
the  preparation  in  question.  Morgen  (9)  experimented  with  a 
circular  piece  of  frog's  stomach,  which  was  suspended  between 
two  metal  hooks  in  a  moist  chamber  while  still  connected  with 
the  mucosa  or  after  freeing  it  of  the  latter,  so  that  the  changes 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  189 

of  form  in  the  ring  of  muscle,  which  was  suitably  loaded, 
could  be  recorded  by  the  graphic  method.  On  exciting  the 
preparation  with  the  constant  current  a  marked  difference 
appeared,  according  as  the  mucosa  was  present  or  absent.  In 
the  first  case  contractions  occurred  plainly  both  on  closing  and 
on  opening  the  circuit ;  but  as  excitability  diminished  in  pre- 
parations that  exhibited  a  certain  degree  of  tonus,  the  break 
excitation  became  more  and  more  prominent — 'its  magnitude 
moreover  increasing  within  a  certain  range  with  the  duration  of 
closure.  After  a  very  long  latent  period  (usually  of  several 
seconds)  the  contraction  began  so  slowly,  that  the  maximum 
was  usually  reached  after  half  a  minute  only.  Eelaxation  then  set 
in  immediately,  proceeding  as  or  even  more  sluggishly.  After 
removing  the  mucous  membrane,  Morgen  noticed  that  the  closure 
contraction,  as  a  rule,  failed  altogether,  and  only  the  opening  of 
the  circuit  was  followed  by  a  marked  shortening.  The  same 
preparation  exhibited  an  analogous  reaction  when  the  animal  had 
been  poisoned  with  morphia.  It  seems  highly  improbable  that 
the  occurrence  of  the  make  contraction  should  in  this  case  be 
associated  with  nervous  elements  (ganglion  -  cells).  It  must 
essentially  be  an  effiect  of  the  tonic  contraction  of  the  muscular 
coat,  increased  by  preparation.  Bernstein,  under  whose  direction 
Morgen's  investigation  was  carried  out,  remarks  further  that 
preparations  which  exhibit  frequent  and  well  -  marked  spon- 
taneous contractions  also  give  very  pronounced  contractions 
at  closure,  while  this  is  not  the  case  with  non-excitable  or  nar- 
cotised preparations. 

It  has  already  been  stated  that  electrical  stimuli  that  are 
ineffective  loer  se,  are,  if  repeated  frequently  at  a  sufficient  in- 
terval, readily  summated  into  an  efficient  excitation,  and 
Engelmann  (I.e.  p.  282)  established  the  same  fact  for  closing,  as 
well  as  for  opening  stimulation  of  the  rabbit's  ureter.  The 
latter  also  occurs  under  certain  conditions  in  the  smooth  muscle 
of  molluscs  (Fig.  80).  On  applying  stronger  currents,  a  new 
and  fu.rther  shortening  is  seen  to  occur  (especially  in  preparations 
not  wholly  relaxed)  after  prolonged  rhythmical  excitation.  There 
can  be  no  doubt  that  this  is  an  opening  contraction,  which  must 
be  explained  by  the  summation  of  intrinsically  ineffective  break 
stimuli,  as  already  pointed  out  by  Tick  in  the  same  connection 
(4,  p.  44  and  p.  50).       We  have  no  hesitation  in  recognising  in 


190 


ELECTRO-PHYSIOLOGY 


this  effect  the  analogue  of  that  "  final  twitch,"  which,  as  we  have 
shown,  sometimes  appears  at  the  end  of  tetanising  excitation  of 
striated  muscle  with  very  frequent  induced  currents,  just  as  the 
"  initial  twitch  "  must  be  regarded,  under  the  same  conditions,  as 
analogous  to  the  closure  twitch  on  excitation  with  the  constant 
current. 

A  fundamental  distinction  between  the  "  twitches  "  produced 
by  single  induction  shocks  and  by  the  closure  or  opening  of  the 
constant  current  is,  as  we  have  already  pointed  out,  the  more 
extended  curve  ("  tetanic  character  ")  of  the  latter.  The  entire 
process  of  shortening  is  prolonged  in  all  its  individual  phases 
(but  especially  in  the  stage  of  falling  energy),  in  correspondence 


_Ijllul]l. 


Fig.  so. — Opening  contraction  (o)  of  adductor  muscle  of  mollusc  (Anodonta)  after  rhythmical 
excitation  with  a  strong  constant  current  (10  Dan.).  Incomplete  tetanus  during  excitation. 
Time-tracing  in  seconds. 


with  the  greater  duration  of  the  make  or  break  excitation.  The 
relations  of  the  latent  period  in  both  cases  is  a  point  of  great 
theoretical  interest.  We  owe  its  thorough  investigation  to 
Tigerstedt  (2),  v.  Bezold  (10)  having  previously  ascertained  that 
the  make  twitch,  with  not  unduly  strong  currents,  has  a  shorter 
latent  period  than  the  make  induction  twitch.  The  difference 
according  to  Tigerstedt  (in  the  non-curarised  gastrocnemius)  is  on 
an  average  0'003  sec.  We  have  invariably  observed  the  same 
results  in  experiments  (to  be  described  below)  on  the  curarised 
sartorius.  In  excitation  with  the  constant  current  the  magni- 
tude of  the  latent  period,  as  shown  by  v,  Bezold,  depends 
essentially  upon  current  intensity,  the  more  so  in  proportion  as 
the  current  used  for  excitation   is  weaker.     If  the  intensity  of 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  191 

current  is  much  increased,  the  effect  on  the  latent  period, 
though  pronounced  at  first,  may  disappear  completely.  In  the 
opening  excitation  the  latent  period,  is  as  a  rule,  longer  than  at 
closure,  so  that  with  weaker  battery  currents  the  difference,  as 
compared  with  induction  twitches,  is  even  more  marked  than 
at  closure.  But  with  increased  current  intensity  and  prolonged 
closure,  it  may  be  almost  entirely  abolished  in  this  case  also. 
In  inquiring  into  the  cause  of  the  shorter  latent  period  in  make 
and  break  induction  twitches,  the  answer  comes  to  hand  when 
we  remember  that  in  order  to  provoke  a  "  twitch,"  a  certain 
acceleration  of  increase  in  the  intensity  of  current  in  the  muscle  is 
essential.  According  to  the  law  proposed  by  du  Bois-Eeymond, 
the  electrical  current  does  not  excite  by  its  absolute  density,  l^ut 
by  its  relative  changes  from  one  moment  to  another,  the  in- 
centive to  movement  consequent  on  these  changes  being  the  more 
considerable  in  proportion  with  their  rapidity  at  uniform  magnitude, 
or  brief  duration  in  a  time-unit. 

And  if,  on  the  other  hand,  we  have  reason  to  suppose  that 
constant  currents  of  medium  strength  undergo  slower  alterations 
of  density  within  the  muscle  than  induction  currents  (in  conse- 
quence of  lower  potential),  then  the  longer  latent  period,  at  least 
for  closure  twitches,  would,  as  Tigerstedt  points  out  {I.e.  p.  197),  be 
dependent  upon  purely  physical  factors,  and  the  self-evident  con- 
sequence of  du  Bois-Eeymond's  "  general  law,"  as  above  stated. 
But  we  haA^e  already  shown  that  the  first  half  at  least  of  this  law 
has  no  application  to  muscle,  and  we  shall  subsequently  find  that 
the  second  half  is  not  generally  applicable  either.  This  does  not 
indeed  cancel  the  possibility  of  explaining  the  above  differences 
in  the  latent  period  as  indicated. 

Here,  we  are  obviously  dealing  with  the  commencement  of 
the  contraction  only,  not  with  its  final  magnitude  and  furtlier 
process.  Although  the  excitatory  effect  of  short,  induced  cur- 
rents is  certainly  less  than  that  of  battery  currents  so  far  as 
regards  magnitude  and  duration  of  the  twitch,  it  is  easy  to  show 
that  the  degree  of  current  density  required  to  produce  a  twitch, 
however  small,  is  more  easily  arrived  at  with  induced,  than  with 
constant,  currents. 

This  leads  us  directly  to  the  question  of  the  de^pendencc  of 
excitatory  effects  upon  the  distribution  in  time  of  the  eleetriccd  move- 
ment.     On  comparing  contractile  substances  collectively,  we  are 


192  ELECTRO-PHYSIOLOGY 


met  by  the  significant  fact  that  rapid  variations  of  density  in 
a  current  are  an  effective  stimulus  to  highly  mobile  kinds  of 
protoplasm  (striated  muscles),  while  they  are  ineffective  towards 
more  sluggish  portions.  This  is  clearly  shown  by  the  fact  that 
normal  striated  muscle,  when  excited  with  the  constant  current, 
twitches  conspicuously  at  the  moment  of  appearance  and  dis- 
appearance (closure  and  opening)  of  the  current.  Tlie  visible 
manifestations  of  persistent  excitation  fall  into  the  hackground, 
vjJiile  the  excitatory  effects  of  current  variation  come  prominently 
foriuard,  in  proportion  as  the  excitcible  protoplasm  is  inore  highly 
motile.  This  dictum  is  sufficiently  borne  out  by  the  total  results 
of  experiments  on  contractile  substance.  It  finds  character- 
istic illustration  when  the  action  of  a  gradually  increasing  current 
on  different  irritable  tissues  is  examined.  If  the  circuit  is  closed 
as  usual  by  hand,  e.g.  with  a  wire  dipping  into  mercury,  the  intensity 
naturally  rises  with  excessive  rapidity  from  zero  to  its  maximum, 
so  that  the  form  of  the  curve  of  variation  is  unrecognisable  in 
detail.  But  by  using  a  contrivance,  by  means  of  which  the 
intensity  of  the  current  can  be  gradually  increased  from  zero — 
as  in  the  slow  and  uniform  gradation  of  the  slider  in  du  Bois' 
rheochord — it  may  easily  be  demonstrated  that  (although  the 
sudden  closure  of  the  same  current  produces  a  maximal  twitch 
with  subsequent  persistent  contraction)  it  now  gives  no  indication 
of  shortening,  or,  in  the  most  favourable  case,  a  weak  persistent 
contraction  only,  in  striated  muscle.  If  the  same  experiment  is 
repeated  on  a  preparation  of  smooth  muscle,  e.g.  the  adductor 
of  the  shell  in  anodonta,  the  effect  is  quite  different.  Pick  (4) 
indeed  asserts  that  he  has  succeeded  "  in  passing  currents  of  con- 
siderable strength  "  through  this  muscle  also,  "  without  contracting 
it,"  but  a  phenomenally  slow  increment  of  current  intensity  was 
required,  extending  over  several  minutes.  Under  these  conditions 
it  can  hardly  be  a  matter  of  surprise  that  no  visible  manifestations 
of  excitation  make  their  appearance,  considering  that  the  effect  of 
the  constantly  increasing  fatigue  changes  in  the  muscle-substance 
must  be  accentuated  in  proportion  with  the  slowness  of  increase 
of  intensity,  at  every  point  at  which  (as  will  be  shown  below)  an 
excitatory  process  is  discharged  by,  and  during,  the  passage  of  the 
current.  At  each  successive  moment,  i.e.,  the  current  acts  upon 
points  of  the  fibre,  which  have  already  been  modified  by  the  whole 
preceding   passage  of  current,  in   proportion  with   its    duration. 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  193 

Moreover,  it  is  easy  to  show,  as  might  be  expected,  that  the 
moUuscan  muscle  in  its  relaxed  state  is  highly  sensitive  to  the 
gradual  entrance  of  current.  If  there  is  a  rheochord  in  the 
circuit,  with  as  many  cells  as  would  be  sufficient  to  set  up  a  strong 
closure  contraction  without  the  rheochord,  an  analogous  change  of 
form  in  the  muscle,  corresponding  with  the  commencement  of  the 
persistent  closure  contraction,  will  invariably  appear  if  the  rheo- 
chord slider  is  gently  pushed  forward  from  the  zero  as  evenly  as 
possible.  The  contraction  begins  when  the  current  has  reached  a 
certain  intensity,  the  curve  rising  the  more  steeply  in  proportion 
with  the  rate  at  which  the  slider  is  pushed  forward.  We  have 
thus  found  it  possible  to  record  marked  effects  when  the  intensity 
of  current  had  been  slowly  increasing  for  two  minutes  ;  the  experi- 
ment of  course  requires  very  sensitive  preparations. 

We  may  conclude  from  the  preceding  data  that  every  change 
of  form  which  can  be  termed  a  "  twitch  "  in  a  suitable  muscle, 
requires  for  its  effective  stimulus  a  more  or  less  rapid  positive  or 
negative  variation  in  current  density,  whether  beginning  at  zero  or 
at  a  finite  value;  and  since,  as  at  once  appears  when  a  muscle 
with  parallel  fibres  is  partially  traversed  by  current  (the  case  of 
total  excitation  will  be  treated  later),  each  twitch  corresponds  with 
a  wave  of  contraction  spreading  through  the  entire  length  of  the 
muscle,  the  transmission  of  excitation  from  the  seat  of  direct 
stimulation  would  seem  in  the  last  resort  to  be  produced  and  con- 
ditioned by  a  rapid  variation  in  the  current.  Hence,  while  strength 
of  excitation  depends  fundamentally  upon  intensity,  duration,  and 
density  of  current,  the  discharge  of  a  ivave  of  contraction  de2Jends  also 
upon  the  nature  {steepness)  of  the  increase  of  current  intensity  in  the 
muscle. 

These  conclusions  stand  out  more  clearly  from  a  simple, 
graphic  representation  (Fig.  81),  after  Fick  (4,  p.  28  f.)  The 
abscissse  indicate  the  times,  the  ordinates  correspond  with  the 
current  intensity  at  the  moment.  While,  in  a  given  case,  a  passage 
of  current,  such  as  is  represented  in  Fig  8 1  (a),  may  fail  to  excite 
both  striated  and  smooth  muscle,  another  process  of  current  like 
Fig  81  (b)  may  be  an  effective  stimulus  for  the  latter.  In 
order  to  produce  the  closure  twitch  in  striated  muscle  a 
steeper  rise  in  the  curve  of  current  density  is  essential.  In 
variations  of  current,  starting  from  and  returning  to  zero,  the 
following  cases  are  conceivable  :  a  variation  of  the  form  (Fig.  81,c,c), 

0 


194 


ELECTRO-PHYSIOLOGY 


corresponding  with  a  single  weak  induction  current,  or  "  current- 
impact/'  does  not  eventually  produce  a  twitch,  as  is  the  case  in  a 
variation  of  the  form  (d),  because  the  low  duration  of  current  is 
compensated  in  the  latter  by  greater  intensity.  On  the  other  hand, 
a  variation  of  the  form  (e)  may  act  as  a  stimulus  on  the  same 
preparation  which  is  unexcited  by  (c),  because  in  this  case  the 
greater  duration  compensates  the  lower  intensity,  and  the  same  may 
also  apply  to  a  variation  with  less  steepness  of  rise  and  fall  (/). 
The    striking  predominance   of  the   excitatory   effect   of  the 


Fig.  81. — «,  b,  c,  Different  forms  of  variation  curves  of  current  intensity.     (A.  Ficlc.)    Tlie  <•     , 
abscissaj  indicate  the  time  in  seconds,  the  ordinates  the  strength  of  current. 

break  induction  current  is  usually  referred  to  the  different  rise 
of  current  intensity,  and  applies  as  much  to  smooth  as  to  striated 
muscle,  and  indeed  to  nearly  all  irritable  tissues.  But  since  the 
experiments  in  this  direction  have  till  now  been  confined  almost 
entirely  to  motor  nerves,  it  will  be  more  convenient  to  postpone 
the  discussion  of  these  facts  until  the  scanty  experimental  data 
which  exist  in  regard  to  dependence  of  excitation  on  the  exact 
form  of  the  curve  of  variation  of  current  intensity  can  be  brought 
forward. 

The  reaction  of  cardiac  muscle  to  the  constant  current,  as 
in  many  other   respects,  is  exceptional.       Ever   since  Eckhardt 


Ill  ELECTRICAL  EXCITATIOX  OF  MUSCLE  195 

(11)  olDserved  the  non-gangiionated  apex  of  the  frog's  heart 
to  -pulsate  rhythmically,  when  a  constant  electrical  current 
was  led  through  it,  this  easily  verified  fact  has  been  the 
subject  of  repeated  experiments.  The  frequency  of  pulsation 
increases  in  a  certam  range  with  the  strength  of  the  current. 
We  have  already  seen  that  cardiac  muscle  responds  by 
rhythmical  manifestations  of  excitation  to  other  continuous, 
uninterrupted  stimuli,  e.g.  mechanical  and  chemical,  so  that 
the  effect  of  sustained  passage  of  current  as  just  described  is 
nothing  extraordinary,  and  the  only  question  is  whether  this 
property  really  is  specific  to  cardiac  muscle,  and  is  not  rather 
a  general  characteristic,  as  it  were  abnormally  developed. 
Hering  (13)  long  ago  observed  that  a  curarised  frog's  sartorius 
became  rhythmically  excited  under  certain  conditions  when  its 
intrinsic  longitudinal  current  was  short  circuited  by  immersion  in 
0"6  ^  NaCl,  and  also  when  acted  upon  by  very  weak  artificial 
currents,  the  reaction  being  similar  to  that  of  chemical  ex- 
citation, according  to  Kiihne  and  Biedermann.  This  however 
only  referred  to  weak  contractions  in  an  unloaded  muscle  that 
was  moreover  dipping  into  fluid.  Later  on  we  succeeded  in 
producing  a  long  series  of  vigorous  twitches,  by  means  of  uniform, 
persistent  closure  of  a  battery  current,  in  a  loaded  sartorius  ex- 
tended in  Hering's  double  myograph,  provided  the  excitability 
of  the  muscle  -  substance  was  locally  increased  at  the  seat  of 
direct  excitation  {i.e.,  as  will  be  shown,  the  kathodic  end  of  the 
muscle)  by  treatment  with  adequate  solutions  of  jS!'a,CO„  from 
1-3  %  (14). 

Fig  82,  a,  shows  such  a  series  of  curves,  recorded  after  fifteen 
minutes'  continuous  action  of  a  2  ^  solution  of  Na.,COg  on 
the  tibial  end  of  a  curarised  sartorius,  during  closure  of  a  medium 
descending  current.  A  rapid  shortening  (twitch)  of  the  muscle 
begins  before  the  first  pronounced  twitch  has  expired,  long  before 
the  descending  shoulder  of  the  curve  has  reached  the  abscissa. 
The  superposition  of  three  twitches  in  rapid  succession  brings  the 
second  contraction  to  the  first  maximum,  after  which  follow  in 
regular  rhythm  twenty -five  vigorous  single  twitches,  hardly 
inferior  in  size  to  the  initial  twitch ;  these,  at  first  closely  packed 
together,  are  discharged  later  at  intervals  of  about  one  second. 
After  the  twentieth  twitch,  the  magnitude  of  shortening  diminishes 
rapidly,  and  at  last  only  a  trace  of  persistent  contraction  remains. 


ELECTRO-PHYSIOLOGY 


which  does  not  disappear  completely 
till  the  current  is  broken.  The  single 
impulses  appear  to  follow  more  quickly 
at  the  beginning  than  later.  Sometimes 
the  rhythmical  twitches  which  are  in- 
duced to  a  certain  extent  by  the  discharge 
of  the  persistent  closure  contraction, 
suddenly  increase  in  height  in  the  course 
of  a  series  of  curves,  so  that  the  line 


Fig.  82. — a,  Two  series  of  rhythmical  twitches,  during  persistent  closure  of  a  battery  cur- 
rent (thermo-electric  pillar,  rheochord  resistance  60),  after  fifteen  minutes'  continuous 
action  of  NaoCOs  (2  %)  on  the  tibial  end  of  the  sartorius ;  b,  second  excitation  of 
same  muscle,  effect  of  fatigue. 

which  connects  the  summits  at  first  rises  steeply,  and  then 
sinks  away  again  rapidly  when  the  height  of  twitch  decreases 
(Fig.  83) — a  reaction  which  recalls  the  well-known  staircase 
increment  of  twitch  in  different  muscles,  on  exciting  them 
with  uniform  induction  currents. 

Since  on  applying  very  strong  currents — according  to 
Hering  very  weak  currents  also — similar  rhythmical  manifesta- 
tions of  excitation,  and  but  little  less  regular,  may  appear  with- 
out any  artificial  increase  of  excitability,  it  is  not  unjustifiable 


ELECTRICAL  EXCITATION  OF  ]\IUSCLE 


197 


to  assume  that  a  sustamed  and  'persistently  flowing  current  in  many 
cases,  jperhaps  always,  sets  up  a  discontinuous  state  of  excitation,  which 
only  produces  an  apparently  steady  contraction,  hecause  the  conditions 
of  experiment  are  usually  such  that  iveak  rhythmical  contractions 
that  are  feehle  in  character  or  confined  to  single  hundles  of  fibres, 
remain  loithout  visible,  mechanical  expression.  From  this  point  of 
view  it  would  be  legitimate  to  speak  of  tetanic  closure  twitches, 
and  of  a  tetanic  character  of  the  persistent  closure  contraction ; 
indeed  it  seems  doubtful  whether  on  exciting  a  curarised  muscle 
with  strong  battery  currents  a  simple  non-tetanic  closure  twitch 


Pig.  S3. — Rhythmical  series  of  twitches  from  sartorius  ;  persistent  closure  of  current ;  gradual 
increment  of  twitches. 


really  can  be  obtained — the  extended  curve  rather  speaks  in 
favour  of  this  view  than  against  it.  How  far  it  is  really  legiti- 
mate to  draw  inferences  from  this  to  the  mode  of  action  of  weaker 
currents  must  provisionally  be  left  undecided,  just  as  it  is  not 
possible  from  our  present  experimental  data  to  postulate  the  dis- 
continuous nature  of  the  persistent  closure  contraction,  although 
there  is  much  to  be  said  for  it.  The  constant  current,  during 
its  closure  in  cardiac  muscle,  thus  produces  a  regular  and  invari- 
able series  of  rhythmical  contractions,  which  also  appear,  at  least 
under  certain  conditions,  in  striated  skeletal  muscle ;  and  this  is 
still  more  the  case  in  smooth  muscle.  Engelmann  (5)  was  the 
first  to  observe  an  appearance  in  the  ureter  of  the  rabbit,  which 
may  be  regarded  as  the  undoubted  analogue  of  the  facts  under 


198  ELECTRO-PHYSIOLOGY 


discussion ;  i.e.  the  periodic  waves  of  contraction  that  start  from 
the  kathode  of  the  constant  current,  without  any  apparent  shift- 
ing of  the  object  upon  the  exciting  electrodes.  "  The  number 
of  contractions  observed  during  a  closure  of  1—2  minutes  was  less 
(2—3)  with  weak  currents,  and  more  (5—7)  with  stronger  currents. 
The  intervals  at  which  the  waves  followed  varied  between  4  and 
20  sees.  The  periods  were  frequently  short  and  equal,  in 
other  cases  they  varied  in  duration.  The  ureter  did  not  usually 
relax  completely  at  the  negative  electrode  in  the  interval  between 
two  waves — at  least  with  the  stronger  currents  (persistent  closure 
contraction)."  At  break  of  the  constant  current  again,  Engelmann 
repeatedly  saw  periodic  waves  of  contraction  starting  from  the 
region  of  the  positive  pole  in  the  rat's  ureter  (I.e.  p.  414),  a 
phenomenon  to  which  we  find  an  analogue  in  the  fact,  that  the 
discharge  of  a  persistent  opening  excitation  in  rhythmical  single 
twitches  may  also  be  observed  in  the  sartorius  under  the 
described  conditions,  though  more  rarely.  As  a  rule,  indeed,  these 
are  only  more  or  less  extended  single  twitches,  and  it  is  im- 
possible to  draw  any  conclusion  as  to  their  tetanic  character. 

N"o  fundamental  difference,  therefore,  obtains  between  the 
manifestations  observed  in  cardiac,  and  in  other,  striated  and 
smooth,  muscle,  during  the  constant  passage  of  current ;  and 
it  is  only  quantitatively  that  differences  can  be  detected  in 
the  rhythmical  discharge  of  excitation,  which  occurs  invariably 
in  the  one  case,  and  in  the  other  only  under  certain  con- 
ditions. The  much  slower  succession  of  single  waves  of  contrac- 
tion in  the  electrical  excitation  of  the  ureter,  is  easily  explained 
by  the  lower  excitability  and  more  sluggish  reaction  of  smooth, 
as  compared  with  striated,  muscle.  And  (as  we  shall  see  below) 
a  similar  relation  obtains  between  this  last  and  the  motor 
nerves,  so  that  the  same  manifestation  presents  itself  in  gradations 
in  the  electrical  excitation  of  smooth  muscle,  cardiac  muscle, 
striated  skeletal  muscle,  and  motor  nerves.  Hence  it  can  be  seen 
that  the  succession  of  rhythmical  excitatory  impulses  is  generally 
more  rapid  in  proportion  as  the  excitability  is  greater.  This 
appears  not  merely  from  the  comparison  of  the  effects  of  excita- 
tion in  smooth  and  striated  muscles,  cardiac  muscle  and  nerve, 
but  also  from  the  phenomena  which  may  be  observed  at  each 
single  excitation  of  any  one  of  these  tissues.  If,  under  the  in- 
fluence of  current,  or  from  any  other  cause,  the  excitability  sinks 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  199 

below  a  certain  limit,  the  possibility  of  rhythmical  sustained 
excitation  disappears  under  all  conditions ;  there  can  be  nothing 
more  than  the  discharge  of  a  single  twitch,  or  the  develop- 
ment of  a  seemingly  sustained  constant  contraction.  We  might 
attempt  to  find  in  these  manifestations  an  exception  to  the 
statement  that  a  "twitch"  (or  self- transmitting  wave  of  con- 
traction) is  only  excited  by  a  more  or  less  steep  variation  in 
intensity  of  the  electrical  current.  But  it  must  not  be  forgotten 
that  this,  in  the  last  resort,  signifies  merely  that  the  changes  pro- 
duced by  current  (as  by  any  other  mode  of  excitation)  in  the 
excitable  substance  must  increase  with  a  certain  rapidity  from 
zero,  or  from  a  finite  value,  if  a  wave  of  contraction  is  to  be 
caused  by  them.  More  or  less  rapid  variations  of  the  state  of 
excitability  of  an  irritable  substance  are  however  conceivable, 
and  really  occur  when  the  cause  of  excitation  itself  is  constant ; 
e.g.  the  pulsations  of  the  apex  of  the  heart  in  chemical  or 
mechanical  excitation.  This  obviously  depends  only  upon  the 
nature  and  state  of  excitability  of  the  substance  in  question. 

We  have  thus  acquainted  ourselves  with  the  dependence  of 
excitation  on  intensity  of  current,  as  well  as  on  its  duration  and 
kind  of  increase  in  general ;  in  conclusion  we  have  to  consider 
the  effect  of  its  direction.  It  is  a  priori  evident  that  this  can 
hardly  play  any  part  in  the  typical,  longitudinal  passage  of 
current  through  a  muscle  with  parallel  fibres,  if  the  muscle 
really  is  constructed  with  geometrical  regularity,  and,  in  parti- 
cular, is  of  equal  diameter  at  both  ends,  so  that  the  density  of 
the  current  at  all  points  will  be  uniform.  Such  preparations, 
however,  are  rarely  met  with,  and  the  generally  adopted  frog's 
sartorius  (although  comparatively  regular)  exhibits  in  this  respect 
considerable  variations.  Before  discussing  this  point  in  detail, 
we  must  consider  the  enormous  influence  exerted  by  the  angle 
of  the  current,  i.e.  the  angle  between  the  lines  of  the  current  and 
the  direction  of  the  fibres. 

The  earlier  observations  on  this  point  were  very  contradict- 
ory. Sachs  (15)  more  especially  maintained  that  muscle  pos- 
sesses equal  excitability  to  transverse  and  to  longitudinal  passage 
of  current,  but  the  method  which  he  employed  leaves  room  for 
doubt  whether  an  electrical  current  traversing  the  muscle  in  a 
really  transverse  direction  can  produce  effective  excitation.  Two 
needles  were  used  in  these  experiments  as  electrodes,  and  brought 


200  ELECTRO-PHYSIOLOGY  chap. 

into  contact  with  the  muscle  in  such  a  way  that  their  line  of  con- 
nection cut  transversely  across  the  muscle-fibres,  so  that  a  current 
passing  through  the  contacts  must  traverse  the  muscle  mainly 
in  a  transverse  direction.  Yet  it  is  almost  self-evident  that 
under  these  conditions,  even  with  the  most  exact  transverse 
passage,  there  must  also  be  longitudinal  lines  of  current.  It 
would  then  depend  merely  upon  the  strength  of  stimulus 
whether  these  were  able  to  provoke  an  excitation.  Sachs  con- 
tended that  the  strength  of  current,  which  is  just  effective  in  his 
experiments,  acted  through  the  lines  of  connection  between  the 
two  electrodes  only,  but  this,  as  was  justly  observed  by  Leicher 
(16),  could  only  occur  under  certain  non-existent  premises. 

A  more  satisfactory  method,  invented  by  Matteucci  in  1838, 
and  then  applied  to  nerve  by  Luchsinger  (17)  at  Hermann's  in- 
stigation, consists  in  plunging  the  object  to  be  traversed  by  the 
current  (nerve  or  muscle)  into  an  indifferent  conducting  fluid, 
which  the  exciting  electrodes  also  dip  into.  In  this  case  the 
muscle,  which  lies  at  right  angles  to  the  lines  between  the  elec- 
trodes, is  entirely,  or  at  least  mainly,  traversed  by  vertical  lines 
of  current  only — entirely  when  the  electrodes  are  fiat  or  linear, 
mainly  when  they  are  punctiform.  Tschirjew  (18),  who  used 
this  method,  found  that  greater  intensity  of  current  is  required 
on  exciting  the  muscle  transversely  than  in  longitudinal  excita- 
tion, but  he  believed  notwithstanding  (taking  into  account 
Hermann's  statement  that  the  resistance  of  the  muscle 
is  much  greater^4— 9  times — in  the  transverse  than  in  the 
longitudinal  direction,  so  that  a  greater  fraction  of  the  cur- 
rent must  pass  through  the  muscle  with  longitudinal  than 
with  transverse  stimulation),  that  muscle  is  more  excitable  to 
transverse  than  to  longitudinal  passage  of  current.  Both  this 
experiment,  however,  and  those  which  Giuffre,  Albrecht,  and 
Meyer  (19)  worked  out  under  Hermann's  direction,  present 
weighty  experimental  objections,  as  Hermann  himself  pointed 
out.  Tschirjew  either  placed  the  excised  muscle  in  the  excitation- 
trough,  with  silk  thread  attached  to  both  ends,  connecting  them 
with  a  lever,  or  employed  minute  quadrants  of  muscle ;  while 
Giuffre  tried  to  avoid  the  difficulties  due  to  irregularities  of  form 
in  the  ends  of  the  muscle  (sartorius)  by  dipping  only  the  portion 
with  parallel  fibres,  which  he  marked  off  with  artificial  transverse 
sections,    into    the    fluid.      Since,   however,   as    will    be    shown. 


in  ELECTRICAL  EXCITATION  OF  MUSCLE  201 

the  excitatory  effect  of  a  current  is  lessened  to  an  extraordinary 
degree  when  it  passes  in  and  out  by  artificial  sections,  or  other- 
wise injured  points  of  the  fibre,  it  is  clear  that  in  all  these  last 
experiments  the  relations  of  excitability  may  appear  to  alter  in 
favour  of  transverse  passage  of  current  under  certain  conditions. 
And  if  a  much  lower  excitability  of  muscle  is  really  found 
to   exist  with    transverse   passage    of    current,   it    can    only   be 


Pig.  84. — Apparatus  for  passing  current  transversely  through  the  muscle  (sartorius).    (Hering.) 
(Catalogue  of  Physiological  Apparatus.    R.  Rothe,  University  Mechanician  in  Prague.) 

viewed  as  an  a  fortiori  proof  that  the  latter  is  a  weaker  stimulus 
than  the  longitudinal  current.  The  point  has  been  experi- 
mentally decided  by  D.  Leicher.  He  used  apparatus,  which  cor- 
responded essentially  with  the  method  employed  much  earlier  by 
Hering  for  the  same  purpose  (Fig.  84).  The  muscle  (curarised 
sartorius)  was  fixed  between  two  clamps  by  the  bones  at  either 
end,  just  as  in  Hering's  double  myograph.  One  clamp  is  fixed, 
the  other  is  left  free,  and  communicates  the  movement  of  the 


202  ELECTRO-PHYSIOLOGY 


musble  to  a  lever.  The  excitation-trough  consists  of  a  parallel- 
epipedic  ebonite  box,  the  shorter  walls  of  which  are  lined  with 
amalgamated  zinc  plates,  which  lead  in  the  current.  At  some 
distance  from  these  are  two  other  walls  of  baked  porous  clay,  so 
that  a  canal  is  formed  on  each  side,  bordering  on  the  some- 
what quadratic  inner  space  of  the  trough.  This  contains  0*6 
y^  NaCl  solution,  while  the  two  canals  are  filled  with  con- 
centrated solution  of  zinc  sulphate.  The  muscle,  conveniently 
stretched  by  a  weight,  and  quite  uninjured,  is  plunged  into  the 
centre  space,  so  that  the  angle  formed  by  the  current  in  its  pass- 
age can  obviously  be  altered  in  any  direction  by  simply  turning 
the  trough  round. 

As  might  be  expected  with  true  longitudinal  passage  of 
current  (angle  0),  the  make  twitch,  or  persistent  make  con- 
traction, appeared,  just  as  outside  the  fluid,  but  Leicher  never 
observed  an  effective  opening  excitation  with  the  strength  of 
current  employed  (9  Dan.)  If  a  current  traverses  the  muscle 
at  an  angle  of  45°,  it  still  has  a  certain  effect,  but  much  less 
than  with  true  longitudinal  passage.  "  Finally,  if  the  muscle 
is  traversed  at  an  angle  of  exactly  90°,  it  usually  remains 
quiescent.  More  rarely  with  transverse  passage  a  weak  excita- 
tion occurs,  which,  notwithstanding  its  inferior  magnitude,  varies 
in  response  to  any  alteration  of  current."  Tlie  total  non- 
excitability  of  striated  muscle  to  electrical  currents  ^perpendicular  to 
the  fibre-axis  must  after  these  simple  demonstrations  be  accepted 
as  proven.  It  is  easy  to  understand  that  the  experiments  in  a 
typical  form  could  only  be  carried  out  on  a  muscle  with 
parallel  fibres  constructed  as  regularly  as  possible,  and  that  any 
preparation  with  a  more  complicated  arrangement  of  fibres  is  a 
23riori  excluded.  There  are  no  corresponding  experiments  on 
smooth  muscular  parts,  but  it  may  be  assumed  that  here  also,  in 
so  far  as  the  contractile  fibrils  run  parallel,  they  give  no  response 
to  the  transverse  passage  of  current.  It  is  clear  that  the  fact  of 
the  dependence  of  excitation  upon  the  magnitude  of  the  angle  at 
which  the  contractile  parts,  lying  in  a  definite  direction,  are 
traversed  by  the  lines  of  current,  is  of  the  greatest  significance  to 
the  theory  of  the  action  of  the  electrical  current.  Before  enter- 
ing upon  this  in  detail  another  fundamental  law  of  electrical 
excitation  must  be  considered,  in  regard  to  the  question  at 
wlioi   point    of   the    tract    in    the    muscle    directly    traversed    an 


Ill  ELECTRICAL  EXCITATIO^^  OF  MUSCLE  203^ 

excitatory  process  is  set  %ip  hy  the  current  at  its  coninuncement 
or  end,  as  tcell  as  during  its  iKtssage.  The  immediate  presump- 
tion which,  at  least  for  induced  currents,  was  for  long  the  only  ac- 
cepted theory,  is  obviously  that  excitation  occurs  uniformly  at  every 
point  of  the  area  traversed,  so  that  when  current  passes  through 
the  muscle  longitudinally,  each  transverse  section  falls  into  simul- 
taneous, and,  in  so  far  as  the  excitability  everywhere  is  equal, 
uniformly  strong  contraction.  The  bare  consideration  of  a 
striated  muscle  stimulated  by  closure  or  opening  of  a-  current 
gives  no  certain  conclusion,  for  there  is  always,  even  in  such 
cases,  an  apparently  simultaneous  shortening  of  the  entire 
muscle,  which  must  be  due  to  an  undulatory  progress  of  the  con- 
traction, as,  e.g.,  in  the  partial  excitation  of  a  muscle  with  parallel 
fibres.  The  question  must  either  be  decided  by  delicate  methods 
of  time-measurement,  as  in  the  determination  of  rate  of  conduct- 
ivity, or  by  experiments  on  muscles  in  which,  as  in  smooth 
fibre-cells,  the  processes  of  contraction  and  conduction  are 
uniformly  slower.  Both  lead  to  the  same  end  eventually.  If 
total  longitudinal  passage  of  current  in  a  parallel-fibred,  cross- 
striated  muscle,  e.g.  sartorius,  produces  excitation  which  is  trans- 
mitted in  undulations  from  one  pole  to  the  other,  it  must 
obviously  be  possible,  by  means  of  two  levers  that  rise  succes- 
sively at  different  points  of  the  muscle,  in  consequence  of  the 
wave  of  contraction  which  passes  under  them,  to  obtain  two 
curves  of  expansion,  which,  when  the  lever  points  lie  vertically 
one  over  the  other,  must  easily  show  whether  the  two  levers  rise 
simultaneously  or  no  ;  in  the  second  alternative,  the  localisation  of 
the  difference  enables  us  to  see  in  which  direction  the  wave  was 
travelling.  Aeby  (20)  tried  to  decide  the  question  experimentally 
on  this  principle.  He  laid  two  levers  on  the  curve  of  the  hori- 
zontally situated  curarised  muscle,  at  a  distance  of  1 7  mm.,  which 
recorded  the  expansion  of  the  muscle,  in  consequence  of  functional 
activity,  on  a  rapidly  rotating  cylinder,  and  found  that  both 
levers  were  simtdtameously  raised  from  the  muscle  when  it  was 
excited  by  the  make  or  break  of  a  constant  current  passing 
through  it.  This  would  to  all  appearance  have  been  impossible 
if  excitation  had  really  started  from  one  end  of  the  muscle  only. 
The  result  of  this  experiment  is  therefore  in  direct  contradiction 
with  the  preceding  theory  of  a  2}olar  excitation  of  the  muscle. 
Von  Bezold  (10)  tried  to  solve  the  problem  by  a  different 


204  ELECTRO-PHYSIOLOGY  chap. 

method  from  that  of  Aeby.  He  employed  the  ordinary  myograph, 
in  which  the  longitudinal  alteration  of  a  muscle  or  fragment  of 
muscle  is  recorded,  using  the  latent  period  of  the  make  and  break 
twitch  as  his  criterion.  The  curarised  sartorius  was  fixed  by 
its  upper  end  to  a  cork  trough  fitted  to  its  size,  so  that  two 
copper  wires  crossing  the  muscle  at  right  angles  to  the  direction 
of  its  fibres  clamped  a  certain  portion  of  its  length,  about  4  mm., 
between  them,  to  two  points  in  this  trough.  The  ends  of  these 
two  wires  served  to  fix  the  muscle  to  the  cork,  and  made  the 
electrodes.  The  portion  of  muscle  between  them  was  thus  at  the 
same  time  the  tract  traversed  by  the  current.  If  the  current 
entered  the  muscle  by  the  lower  electrode,  nearest  to  the  record- 
ing end,  i.e.  was,  as  v.  Bezold  expresses  it,  an  ascending  current, 
the  resulting  curve  showed  that  a  longer  time  elapsed  between  the 
moment  of  closure  and  the  beginning  of  the  twitch  than  when  the 
current  left  the  muscle  by  the  lower  electrode,  i.e.  was  descending. 
In  the  first  case,  according  to  Bezold,  the  excitatory  wave  arising  at 
the  upper  (negative)  electrode,  had  to  spread  itself  over  the  intra- 
polar  tract,  which  was  fixed  at  both  sides,  before  it  could  enter  the 
free  portion  of  the  muscle  below  and  through  the  lower  (positive) 
electrode ;  in  other  cases  the  excitation  started  from  the  lower 
electrode  (which  was  now  negative),  and  passed  immediately  over 
to  the  free  part  of  the  muscle.  The  difference  in  the  two  times 
which  elapse  between  the  moment  of  closing  the  current  and  the 
beginning  of  the  twitch  corresponded  to  the  time  required  by 
the  excitation  to  traverse  the  intrapolar  tract  of  4  mm.  Von 
Bezold  showed  by  the  same  method  that  on  opening  the  circuit 
the  excitation  started  at  the  positive  electrode.  Aeby  disputed 
the  conclusions  of  v.  Bezold's  experiments,  but  as  Hering 
remarks  {I.e.  p.  248),  it  is  impossible  to  account  for  the  time 
differences  found  by  v.  Bezold,  and  constantly  recurring  in  the 
same  sense,  in  any  other  way  than  by  the  different  direction  of 
the  current.  The  marked  variation  in  magnitude  of  time- 
difference,  amounting  to  between  0'005  and  0'025  (average 
0"012)  sees.,  is  perhaps,  according  to  Hering,  to  be  explained  by 
the  fact  that  the  conductivity  of  the  muscle  is  disturbed  in  a 
different  degree  at  the  part  clamped,  according  to  the  amount  of 
pressure  put  upon  it.  Taking  for  granted  then  that  the  time 
from  the  moment  of  closure  or  opening  to  the  beginning  of  the 
contraction  is  really  longer  when  the  upper  contact  makes  the 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  205 

kathode  at  closure  and  the  anode  at  opening,  it  may  further  Ije 
asked  how  far  the  different  direction  of  current  accounts  for 
this  disparity.  This  question,  however,  is  answered  by  v. 
Bezold's  hypothesis,  according  to  which  the  direct  conckision 
from  the  above  experiment  is  as  follows :  "  That  on  the  closure  of 
a  constant  current,  {striated)  muscle  is  at  first  excited  in  the  region 
of  the  negative  electrode  and  not  in  the  region  of  the  positive 
electrode,  luhile  on  o'pening  the  current  flowing  through  the  muscle, 
the  immediate  excitation  woidd  tc  at  the  positive  and  not  at  the 
negative  ijole." 

These  data  of  v.  Bezold,  and  the  conclusions  drawn  from 
them,  are  borne  out  by  the  well-known  fact  that,  on  exciting 
with  the  constant  current  under  certain  conditions  {i.e.  diminished 
conductivity),  the  manifestations  of  contraction  are  confined  to 
the  region  of  the  point  at  which  the  current  leaves  the  muscle 
(kathode),  and  that  this  occurs  invariably  in  the  persistent 
closure  contraction  when  currents  that  are  not  unduly  strong  are 
sent  into  the  muscle.  With  reference  to  the  first  point,  v. 
Bezold  refers  back  to  an  older  observation  of  Schiff  (21),  who 
found  that  when  a  moribund  muscle  had  already  ceased  to  yield 
a  closure  twitch  there  was  still  at  the  negative  pole  of  a  constant 
current  a  weak,  localised  idio-muscular  contraction,  far  less  dis- 
tinctly expressed  than  the  effect  of  mechanical  excitation,  which 
persists  uniformly  so  long  as  the  current  continues,  and  then  dies 
away  again.  It  is  not  difficult  to  show  that  this  "idio- 
muscular  "  kathodic  persistent  contraction  is  completely  identical 
with  the  persistent  closure  contraction  described  above,  provided 
the  currents  used  for  excitation  are  not  excessively  strong. 
Engelmann  (5)  obtained  direct  experimental  proof  that  in 
perfectly  fresh  muscle  also  the  sustained  contraction  following 
on  the  closure  twitch  is  confined  to  the  region  of  the  kathode. 
The  method  of  his  experiment  is  evident  from  the  accompanying 
diagram  (Fig.  85).  Engelmann  passed  a  current  through  the 
entire  sartorius,  and  fixed  the  upper  section  with  a  clamp  which 
was  7  mm.  or  more  below  the  upper  electrode,  while  the  lower 
electrode  was  formed  by  a  wire  hook  introduced  into  the  muscle. 
The  section  of  muscle  below  the  clamp  was  therefore  the  only 
movable  part,  and  recorded  its  contractions  upon  a  slowly 
travelling  surface.  When  the  current  in  the  muscle  was 
descending,  the  lever  remained  above  the  abscissa  after  the  make 


206 


ELECTRO-PHYSIOLOGY 


twitch  had  exph'ed,  as  long  as  the  closure  lasted ;  when,  on  the 
other  hand,  it  was  ascending  the  lever  returned  to  the  abscissa 
completely  after  this  twitch.  By  the  same  method  of  experi- 
ment, moreover,  it  is  easy  to  establish  v.  Bezold's  conclusions.  In 
two  experiments  Engelmann  found  that  the  closure  twitch  began 
0'006  sees,  and  0'009  sees,  later  with  an  ascending  than  with  a 
descending  current,  which  must  be  explained  by  saying  that  in 
the  ascending  current  the  contraction  discharged  at  the  upper 
end  of  the  muscle  must  first  be  transmitted  through  a  tract  of 
muscle  7  mm.  long  before  it  can  act  upon  the  lower  movable 
section  of  the  muscle.  The  localisation  of  the  closing,  as  well 
as    opening,   persistent  contraction,   is   elegantly   shown   by  the 


following  method,  taken  from  Engelmann.  The  curarised 
sartorius  is  extended  in  Hering's  double  myograph,  with  non- 
polarisable  electrodes,  which  in  this  case  are  loth  free.  In  order 
to  observe  the  changes  of  form  independently  in  either  half  of 
the  muscle,  its  centre  is  fixed  by  a  clamp  specially  constructed 
for  the  purpose.  This  consists  of  two  troughs,  not  exceeding  5 
mm.  in  length,  supported  by  a  pillar,  and  covered  with  a  layer 
of  oil  clay  (Eig.  71).  The  clay  moulds  itself  firmly  to  the 
shape  of  the  muscle,  holding  it  sufficiently  by  contact  alone, 
with  no  perceptible  pressure,  to  prevent  a  direct  transfer  of  the 
changes  of  form  from  one  half  of  the  muscle  to  the  other,  without 
inhibiting  the  transmission  of  the  excitatory  process.  The  non- 
polarisable  electrodes  make  it  possible  to  continue  the  passage 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  207 

of  current  through  the  muscle  as  long  as  is  required,  without  any 
fear  of  the  intensity  of  the  current  diminishing  in  a  perceptible 
degree ;  and  this  is  facilitated  by  the  study  of  the  persistent 
opening  contraction.  It  is  at  once  seen  that  first  one  and 
then  the  other  half  of  the  muscle,  according  to  the  direction  of 
the  current  flowing  through  it,  becomes  permanently  shortened 
(Fig.  88),  and  that  on  strengthening  the  current  the  persistent 
contraction  increases  considerably  (Fig.  78),  without  any  transfer 
to  the  other  (anodic)  half.  If  a  muscle  that  is  not  too  tensely 
stretched  is  examined  with  the  unaided  eye  or  magnifying  lens, 
the  local  swelling  of  the  ends  of  the  fibres  may  be  plainly 
seen,  even  with  minimal  currents,  after  the  closure  twitch  has 
expired,  as  described  by  Engelmann.  The  contractile  substance 
almost  appears  to  flow  suddenly,  as  it  were,  at  the  moment  of 
closure,  from  the  region  round  the  kathode  to  the  kathode  itself, 
and  to  accumulate  there.  In  muscles  that  have  been  exposed  to 
excess  of  cooling,  by  which  their  conductivity  has  suffered,  it  can 
be  seen  directly,  as  shown  by  Hermann,  that  the  muscle  is  drawn 
at  closure  towards  the  kathode,  on  opening  towards  the  anode. 
The  swelling  only  affects  the  peripheral  ends  of  the  fibres, 
immediately  before  they  pass  into  the  tendon.  Even  with 
moderately  great  tension  of  the  muscle,  a  small  swollen  expan- 
sion appears,  which  persists  unchanged  throughout  the  entire 
duration  of  a  persistent  passage  of  current.  On  strengthening 
the  excitatory  current  the  persistent  closure  contraction  increases 
considerably  in  amplitude,  without  however  losing  its  localised 
character,  even  with  high  intensity  of  current.  The  sections 
which  lie  collectively  between  the  kathode  and  the  centre  of  the 
muscle  never  remain  in  persistent  contraction  during  the  passage 
of  current.  In  judging  of  the  spatial  extension  of  a  manifesta- 
tion of  contraction  in  muscle,  great  care  must  be  taken  not  to 
confound  the  true  shortening  with  the  merely  passive  contraction 
of  adjacent  parts.  A  very  simple  method  of  artificial  observation 
consists  in  marking  the  surface  of  the  muscle  with  signs,  which 
move  in  opposite  directions  when  the  muscle  shortens,  and  thus 
indicate  the  spatial  extension  of  the  contraction.  We  have  found 
it  convenient  to  paint  the  whole  muscle  with  transverse  bands  of 
Indian  ink,  at  right  angles  to  the  direction  of  the  fibres,  so  that 
the  distance  between  each  pair  of  cross-lines,  traced  with  a  fine 
bristle  upon  the  dry  surface  of  the  sartorius,  was  about  i  mm. 


208  ELECTRO-PHYSIOLOGY 


Each  contraction,  however  small,  was  then  defined  by  a  more  or 
less  considerable  reduction  in  one  or  more  of  the  cross-bands  or. 
the  coloured  spaces  between  them.  Within  the  passively  partici- 
pating muscle  tracts,  on  the  other  hand,  the  coloured  cross-bands 
are  much  contorted,  but  do  not  appear  to  get  smaller.  In  very 
widely  extended  tracts  they  grow  considerably  broader,  as  will 
appear  below  (22). 

In  a  tracing — conformably  with  direct  observation — the 
persistent  closure  contraction  only  appears  in  the  curve  correspond- 
ing with  the  kathodic  half  of  the  muscle,  but  if  the  currents 
employed  are  not  too  strong  (Figs.  77  and  78)  the  closure  twitch 
is  seen  on  both  sides  equally.  It  is  only  with  the  weakest  minimal 
currents  that  the  twitch  appears  higher  on  the  kathodic  than  on  the 
anodic  side,  where  it  is  sometimes  no  more  than  a  little  hump. 
This  marked  difference,  which  is  plain  with  the  application  of  the 
weakest  currents,  occasionally  persists  for  a  considerable  period, 
disappearing,  however,  as  a  rule  (provided  the  excitability  and 
conductivity  of  the  muscle  have  not  otherwise  suffered),  at  an 
intensity  of  current  which  may  still  be  termed  low,  giving  place  to 
complete  uniformity  of  twitch  on  either  half  of  the  muscle.  The 
assumption  that  the  mechanical  conditions  of  shortening  are  less 
favourable  in  the  one  half  than  in  the  other  is  easily  shown  by 
control  experiments  to  be  inadequate,  so  that  the  behaviour  of  the 
sartorius  towards  the  weakest  minimal  closure  stimuH,  as  described, 
is  no  less  calculated  to  confirm  v.  Bezold's  theory  of  the  seat  of 
direct  excitation  by  the  current,  than,  with  application  of  stronger 
currents,  the  fact  of  localisation  of  the  persistent  closure  con- 
traction. These  experiments  show  further  that  the  waves  of 
excitation,  i.e.  contraction,  may  die  out  on  passage  through  the 
intrapolar  tract  if  the  discharging  stimulus  is  very  weak,  and 
that  with  somewhat  stronger  stimuli  they  are  propagated  in 
a  diminishing  degree  (with  a  decrement)  in  the  anodic — or,  at  the 
opening  excitation,  kathodic — half  of  the  muscle.  This  is  quite 
evident  in  a  prolonged  series  of  twitches  obtained  by  repeated 
closure  at  uniform  strength  and  direction  of  current.  Here  the 
height  of  the  curve  of  the  twitches  decreases  more  rapidly  than  the 
magnitude  of  the  sustained  contraction,  which  still  appears  at  each 
new  closure,  even  when  the  make  twitch  has  completely  died  out 
on  the  kathodic  side.  On  the  other  hand,  the  unequal  decrease 
in  the  height  of  the  closure  twitch  on  the  kathodic  and  anodic 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  209 

sides  respectively  is  very  apparent  during  the  process  of  "  fatigue"; 
both  curves  are  ahnost  equal  in  height  at  the  beginning.  The 
anodic  twitch  is  later  only  half  as  high  as  on  the  kathodic  side, 
and  finally  disappears  altogether,  while  the  latter  is  still  twitching 
visibly  (Fig.  77).  If  the  intensity  of  current  exceeds  a  certain 
limit  there  is  regularly  an  apparent  invasion  of  the  persistent 
closure  contraction,  which  starts  at  first  from  the  kathodic 
end  only,  and  spreads  over  the  fixed  centre  of  the  muscle. 
This  phenomenon  is  most  conspicuous  with  currents  that  are 
inadequate  to  produce  an  effective  break  excitation  at  the  usual 
period  of  closure.  It  is  very  remarkable  that  the  degree  of 
persistent  shortening,  is  not,  as  might  a  iwiori  be  expected, 
under  all  conditions  higher  on  the  kathodic  side  than  on  that  of 
the  anode,  but  xoith  currents  of  a  certain  strength  the  ratio  is  usualli/ 
oAigmented.  Aeby  (20)  drew  attention  to  an  analogous  relation 
for  the  closure  twitch,  when  he  found  that  the  ratio  of  height  of 
twitch  in  either  half  of  the  muscle  was  inverted  with  stronger 
currents,  and  under  the  influence  of  progressive  fatigue — the 
twitches  of  the  anodic  half,  which  at  the  beginning  were  equal 
with  or  smaller  than  those  of  the  kathodic  half,  gradually  becom- 
ing larger  than  the  latter.  Indeed  it  may  happen  that — con- 
versely to  the  case  of  currents  of  medium  intensity — the  kathodic 
half  will  exhibit  only  a  weak  sustained  contraction,  while  the 
anodic  half  still  twitches  plainly  at  each  new  closure. 

The  asymmetry  of  the  sartorius  is  very  disturbing  in  all 
these  experiments,  since,  as  we  shall  see,  it  produces  an  a 
loriori  ineqviality  of  excitation  effects  in  the  two  halves  of  the 
muscle,  with  alternating  direction  of  currents.  This  agrees  with 
the  fact  that  the  diffusion  of  the  persistent  closure  contraction 
over  both  halves  of  the  muscle  already  referred  to  always  shows 
itself  earlier,  and  is  much  more  marked,  with  an  ascending; 
direction  of  current  {i.e.  from  knee  end  to  pelvic  end),  than 
with  a  descending  current.  This  is  the  more  remarkable  since, 
in  consequence  of  the  increasing  density  at  the  small,  tapering, 
lower  end  of  the  muscle,  and  the  more  pronounced  make  excita- 
tion produced  by  it  with  a  descending  direction  of  current,  the 
opposite  might  rather  have  been  expected — if  with  increase  of 
current  the  magnitude  of  the  make  twitch  and  the  degree  of 
diffusion  of  the  persistent  closure  contraction  really  depend 
essentially    upon    the    strength    of    excitation    at    the    kathode. 

P 


210  ELECTRO-PHYSIOLOGY 


But,  as  we  shall  see  later,  the  sustained  contraction  appearing 
under  these  conditions  in  the  anodic  half  of  the  muscle  is  really 
a  manifestation  sui  generis,  and  does  not  stand  in  any  causative 
connection  with  the  normal  persistent  kathodic  closure  contraction 
at  the  ends  of  fibres.  With  regard  to  the  localisation  of  the 
hreak  excitation,  we  must  further  remark  that  it  takes  effect  at 
the  anode  in  exactly  the  same  way  as  the  make  excitation 
at  the  kathode,  since  at  first  only  the  corresponding  half  of 
the  muscle  twitches,  and  it  is  only  later,  when  the  excitation  at 
the  anode  has  reached  a  certain  magnitude,  that  the  wave  of  con- 
traction propagates  itself  through  the  entire  muscle,  and  this  with 
a  perceptible  decrement,  expressed  in  the  different  height  of 
twitch  in  either  half.  The  persistent  opening  contraction  is 
similarly  localised  in  the  region  surrounding  the  point  where  the 
current  enters. 

With  the  exception  of  the  persistent  closure  contraction  on 
the  side  of  the  anode,  occurring  as  described  under  certain  con- 
ditions only,  it  cannot  be  denied  that  the  facts  above  stated  are 
collectively  much  in  favour  of  v.  Bezold's  view  of  a  polar  excitation 
of  muscle  by  the  current.  Notwithstanding  this,  however,  the 
localisation  of  the  closing  and  opening  persistent  contraction 
cannot  be  taken  ijer  se  as  a  strong  proof  of  its  validity.  For  if 
the  persistent  closure  contraction  seems  to  be  localised  in  the 
region  round  the  point  of  exit  of  the  current,  the  objection  may 
be,  and  actually  has  been,  made  (Brlicke,  23),  that  the  current 
has  an  excitatory  action  upon  the  whole  tract,  taking  further 
into  consideration  that  this  direct  excitation  in  the  region  of 
the  anode  soon  becomes  ineffective  in  consequence  of  a  depression 
of  excitability  proceeding  from  the  same  region.  Against  this, 
again,  there  is  the  extraordinarily  limited  diffusion  of  the  persist- 
ent kathodic  closure  contraction,  as  is  readily  ascertained  from  mere 
inspection.  It  appears  desirable  to  collect  more  evidence, 
and  in  particular  to  determine  positively  the  fact  that  at  each 
closing  twitch  a  wave  of  contraction  proceeds  from  the  kathode, 
at  each  opening  twitch  from  the  anode.  Here,  again,  the  method 
of  clamping  the  muscle  by  its  centre,  as  described  above,  affords 
excellent  experimental  possibilities. 

Before  entering  more  minutely  into  the  question  it  will  be  as 
well  to  determine  the  fundamental  point  of  what  is  to  he  under- 
stood in  the  electrical  excitation  of  a  muscle  hy  kathode  and  anode. 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  211 

In  the  majority  of  the  okler  experiments,  where  the  current  was 
led  in  through  metal  wires,  in  direct  contact  with  the  muscle,  there 
can,  of  course,  be  no  doubt  as  to  the  meaning  of  the  terms  anode 
and  kathode.  So,  too,  in  v.  Bezold's  experiments,  the  expression 
"  the  closing  excitation  proceeds  from  the  kathode,  the  opening 
excitation  from  the  anode,"  cannot  well  be  misunderstood.  But  the 
case  is  otherwise  when,  although  metal  conductors  are  used,  the 
current  is  led  into  the  muscle  via  bones  and  tendons.  Then  the 
expression  quoted  takes  on  quite  another  meaning.  It  is  obvious 
that  the  excitation  cannot  proceed  in  this  case  from  those  points 
at  which  the  metallic  electrodes  are  in  contact  with  animal  tissues, 
e.g.  the  bones  or  tendons ;  but  that  the  tendinous  ends  of  the 
muscle-fibres  themselves  are  the  real  electrodes,  and  when,  under 
these  circumstances,  electrodes  are  spoken  of,  it  can  only  mean 
that  the  current  sets  up  a  peculiar  action  at  the  points  at  luliich 
it  enters  or  leaves  the  muscle-fihres.  How  easily  misunderstandings 
may  arise  through  these  ambiguities,  is  evident  from  the 
consideration  of  certain  experiments  of  Aeby  (20)  and  Brlicke 
(23),  which  are  intended  to  disprove  v.  Bezold's  theory.  The 
former  sent  current  through  both  legs  of  a  frog  still  united  by 
the  pelvis,  so  arranged  that  the  wires  which  served  as  electrodes 
were  connected  with  the  lower  ends  of  the  two  legs.  A  piece  of 
the  thigh-bone  was  cut  out  on  either  side  subcutaneously,  so  that 
the  muscles  of  both  thighs  shortened  at  closure  of  the  current, 
but  more  so  with  a  descending  than  with  an  ascending  current. 
Aeby  deduced  from  this  that  the  former  lay  nearer  to  the 
negative — as  he  thought,  more  active — pole  ;  thereby,  as  Engel- 
mann  pointed  out,  confusing  the  real,  or  natural,  electrodes  of  the 
muscle  with  the  artificial — i.e.  unreal — electrodes  of  the  entire 
preparation.  For  obviously,  in  a  thigh  traversed  by  an  ascending 
current,  the  anode  would  occur  at  the  knee,  the  kathode  at  the 
pelvis,  and  vice  versa  in  opposite  cases.  Briicke  used  a  similar 
preparation,  only  he  removed  the  entire  skin,  with  the  extensor 
muscles,  together  with  the  diaphyses  of  the  thigh-bones.  If  he 
gripped  the  two  gastrocnemii  with  forceps,  connected  in  circuit 
with  6—10  small  Daniell  cells,  the  muscles  of  the  thio-h  and  leo- 
contracted  on  both  sides.  "  In  this  case,"  says  Brticke,  "  no 
contraction  waves  could  spread  from  the  kathode  to  the  flexors 
of  the  thigh.  It  must  be  admitted  that  they  contracted  independ- 
ently of  all  kathodic  action,  solely  because  they  were  traversed  by 


212  ELECTRO-PHYSIOLOGY 


the  current ;  otherwise  it  must  be  assumed  that  the  knee-joint  on 
the  kathodic  side,  or  the  remains  of  the  pelvis  on  the  anodic,  act 
as  kathode  for  the  thigh  muscles."  But  as  Hering  showed,  this 
view  is  that  which  was  long  ago  opposed  by  Engelmann,  since  for 
him  the  anode  is  the  place  where  current  enters  the  muscle-fibres, 
the  kathode  the  place  at  which  it  leaves  them.  Hering  {I.e. 
p.  241)  expresses  this  more  exactly  as  follows  :  the  real  'physiolo- 
gical anode  in  the  musele  is  formed  hy  the  collective  points  at  which 
current  enters  the  contractile  substance  ;  the  physiological  hathode  hy 
the  collective  points  at  lohich  it  leaves  them. 

This  proposition  leads  to  a  corollary,  best  expressed  in  Bering's 
own  words.  "  If  we  picture  the  entire  current  which  traverses 
the  muscle  longitudinally  to  be  divided  into  single  lines  of  cur- 
rent, these  would  indeed,  generally  speaking,  lie  parallel  with  the 
direction  and  limits  of  the  single  fibres  in  a  parallel-fibred  muscle, 
and  the  collective  anodic  points  would  lie  at  one  end,  the  collect- 
ive kathodic  points  at  the  other,  of  the  muscle ;  in  detail,  how- 
ever, there  would  be  innumerable  exceptions.  In  the  first  place, 
quite  apart  from  any  tendinous  intersections,  we  must  consider 
the  case  in  which  the  single  muscle-fibres  end  at  different  points 
of  the  muscle,  although  the  bulk  of  them  may  be  approximately 
as  long  as  the  muscle  itself.  But  directly  such  muscle-fibres 
occur,  the  points  at  which  the  current  enters  or  leaves  are  no 
longer  to  be  sought  exclusively  at  the  ends  of  the  muscle,  and 
besides  the  chief  centres  of  polar  current  action,  other  centres 
will  be  distributed  in  the  muscle. 

"  Moreover  an  absolute  parallelism  between  the  lines  of 
current  and  the  muscle-fibres  cannot,  as  a  rule,  be  predicated, 
particularly  where  the  muscle  is  not  extended,  or  is  subjected 
to  pressure  at  any  spot,  or  if  its  surface  is  not  entirely  freed 
from  the  remains  of  adherent  conducting  matters,  solid  or  fluid. 

"  In  muscles  which  are  lying  relaxed  upon  a  slide,  the  fibres, 
as  we  know,  by  no  means  invariably  run  straight,  but  are  often 
undulatory,  especially  after  a  preceding  twitch  of  the  muscle, 
because  they  cannot  elongate  again  on  account  of  the  friction  on 
their  under -surface.  A  current  traversing  the  muscle  longi- 
tudinally would  then  find  innumerable  points  of  entry  and  exit 
along  the  edges  of  each  individual  muscle-fibre,  and  it  would  be 
quite  fallacious  to  place  the  physiological  anode  and  kathode 
exclusively  at  the  ends  of  the  muscle.      If  the  muscle  is  clamped 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  213 

at  any  point  of  its  course,  considerable  bending  of  part  of  the 
muscle-fibres  is  inevitable,  especially  if  the  muscle  is  pressed 
between  two  forks,  with  converse  surfaces.  The  same  thing 
occurs  when  a  lever  or  button  is  placed  on  the  muscle,  and  presses 
on  it  at  the  points  of  contact.  In  all  these  cases,  part  of  the 
current  must  pass  in  and  out  of  the  contractile  substance  in  a 
number  of  muscle-fibres  at  the  seat  of  pressure." 

These  observations  will  show  why  the  negative  results  of 
Aeby's  experiments  {siipra) — in  which,  when  a  parallel-fibred 
muscle  is  wholly  traversed  by  current,  the  propagation  of  a  con- 
traction wave  is  demonstrated  by  a  lever — cannot  be  regarded 
as  conclusive  against  the  positive  results  of  v.  Bezold.  In  Aeby's 
experiments,  a  very  considerable  bending  of  fibres  occurs  at  both 
points  at  which  the  lever  is  laid  upon  the  muscle.  Aeby  him- 
self remarks  that  "  the  lever  was  pressing  somewhat  upon  the 
surface  of  the  muscle."  So  that  the  current  at  the  point  at  which 
the  fibres  bend  inwards  may  very  well  pass  in  and  out  at  different 
points  of  the  contractile  substance,  and  thus  produce  a  direct 
excitation. 

Under  these  conditions,  new  experiments  re  the  polar 
effects  of  the  electrical  current  appeared  desirable.  The 
clamp  experiment  (Engelmann)  with  the  frog's  sartorius,  as 
described  above,  in  which  the  excitation  passes  the  fixed  point 
without  difficulty,  while  the  direct  transmission  of  contraction 
from  one  half  of  the  muscle  to  the  other  is  made  quite  impossible, 
affords  a  simple  method  of  graphically  recording  the  course  of  the 
contraction  wave,  and  so  making  measurement  possible ;  for  if 
excitation  starts  from  the  kathode  on  closure  of  the  current,  a 
muscle,  fixed  in  this  manner,  and  traversed  by  current  in  its 
entire  length,  must  twitch  in  the  half  corresponding  with  the 
kathode  earlier  than  the  anodic  half.  The  latter  only  begins  to 
shorten  when  the  wave  of  contraction  proceeding  from  the  kathode 
has  passed  beyond  the  clamped  part.  The  time  difference  at  the 
beginning  of  the  contraction  of  the  two  halves  obviously  corre- 
sponds with  the  rate  of  transmission  of  the  excitation,  i.e.  contrac- 
tion wave,  from  the  kathodic  end  to  the  first  section  beyond  the 
clamp. 

The  method  of  experiment  was  as  follows :  a  tuning-fork, 
making  353  vibrations  per  sec,  and  provided  with  a  lever,  served 
as  the  time-marker.      This,    together   with  a   double  myograph, 


214 


ELECTRO-PHYSIOLOGY 


with  non-polarisable,  movable  electrodes,  stood  in  front  of  a  ver- 
tical cylinder,  which  turned  upon  a  crank,  and  the  contractions  of 
both  halves  of  the  muscle  were  recorded  on  its  smoked  surface, 
so  that  the  point  of  the  tuning-fork  lever  lay  vertical  to  the  two 
muscle  levers,  which  move  (up  and  down)  in  opposite  directions ; 
in  this  way  it  is  possible,  independent  of  the  rate  at  which  the 
cylinder  rotates,  to  measure  the  difference  in  time  between 
the  beginning  of  the  two  twitches  as  well  as  the  period  of 
latent  excitation,  if  the  experiment  is  arranged  so  that  the  tuning- 
fork  begins  to  vibrate  at  the  precise  moment  of  closure  or  opening 
of  the  current,  as  may  easily  be  effected  by  withdrawing  a  con- 
ducting wedge  introduced 
between  the  limbs  of  the 
fork  (Fig.  86). 

By  this  method  two 
curves  of  twitch  are  ob- 
tained with  the  closure 
of  a  battery  current  of 
sufficient  intensity,  one 
traced  upwards  and  the 
other  downwards,  which 
are  always  in  such  rela- 
tions with  each  other  that 
the  curve  corresponding 
with    the    kathodic    half 

Fig.  S6.— Registering  tuning-fork,  for  interruption  Qf    the    niUSClc    riseS    13er- 

or  closure  of  current.    (Hering.) 

ceptibly  earlier  from 
the  abscissa  than  the  other  (Fig.  87,  a,  h). 

If  a  perpendicular  is  drawn  from  each  abscissa  at  the  point  at 
which  the  curve  commences,  the  number  of  tuning-fork  vibrations 
enclosed  between  the  two  perpendiculars  gives  the  rapidity  at 
which  the  wave  of  contraction,  measured  from  its  point  of  origin 
at  the  kathode  to  the  first  muscle  section  beyond  the  fixed  spot, 
is  transmitted.  The  length  of  this  tract  is  20—27  mm.  according 
to  the  size  of  the  frog ;  this  corresponds  with  4—6  vibrations 
of  the  tuning-fork,  and  the  velocity  of  the  make  excitation  is 
therefore  1—2  m,  per  sec. 

The  same  method  may  be  employed  to  investigate  the 
time -relations  of  the  break  excitation.  Since  the  denervated 
muscle  reacts  more  slowly  to  the  break  stimulus,  the  intensity  of 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  215 

current  must  be  considerably  higher.  Moreover,  as  we  have  seen, 
the  duration  of  current  is  of  great  moment ;  at  break  excitation, 
the  anodic  half  of  the  muscle  invariably  begins  to  twitch  before 
the  kathodic  half,  and  the  two  curves  seem  in  this  way  to  be 
relatively  altered  (24). 

Constant  currents  of  very  short  duration  (current  impacts) 
and  single  induction  shocks  are,  as  a  rule,  effective  only  at  their 
commencement,  and  not  at  the  termination  of  the  current.  Chau- 
veau  observed  in  the  muscles  of  living,  warm-blooded  animals, 
that  weak  induction  currents,  and  currents  from  a  Leyden  jar, 
excite  primarily  in  the  kathodic  region,  and  Engelmann  emphasises 
the  entire  correspondence  of  action  between  short  battery  currents 
and  single  induction  shocks,  showing  that  an  induction  shock  sent 
through  a  long  strip  of  rabbit's  ureter  at  most  discharges  a  wave 
of  contraction  at  the  seat  of  the  kathode,  while  it  is  only  with 
very  great  excitability,  and  currents  of  marked  intensity,  that 
contraction  sometimes  appears  to  begin  simultaneously  at  both 
poles.  It  is  not  difficult  to  demonstrate  the  same  effect  in 
striated  muscle  with  similar  excitation.  If  the  curarised  frog's 
sartorius  is  again  experimented  on,  and  excited  by  a  fresh 
induction  shock,  the  curve  of  twitch  corresponding  with  the 
kathodic  half  will  always,  after  a  brief  latent  period,  rise  earlier 
from  the  abscissa,  than  that  corresponding  with  the  anodic  half, 
in  the  muscle  stretched  in  the  double  myograph,  and  clamped  in 
the  middle. 

With  higher  intensity  of  induction  currents,  however,  the 
anodic  break  stimulus  also  seems  to  become  effective,  which  is 
not  surprising  after  Engelmann's  experiments  on  the  ureter. 
Eegeczy  (25)  fixed  the  sartorius  like  Engelmann  by  clamping  it 
in  the  centre  more  or  less  firmly  with  ivory  forceps,  the  other 
end  being  immovably  fixed  by  another  forceps  ;  the  lower  end  was 
connected  with  the  lever  of  the  myograph.  The  lower  electrode 
was  connected  with  the  forceps  fixed  to  the  centre  of  the  muscle, 
the  upper  one  was  attached  to  the  upper  end  of  the  muscle  (cf. 
Fig.  85).  The  direction  of  the  induction  current  (coil  at  maximum 
strength)  can  be  changed  by  a  reverser.  ISTo  difference  was  found  in 
the  size  of  the  latent  period  with  ascending  or  descending  currents, 
as  might  have  been  expected  from  the  experiments  of  v.  Bezold, 
Engelmann,  and  Biedermann,  with  battery  currents.  While  with 
weak  induction  currents  the  excitation  starts  from  the  kathode 


216  ELECTRO-PHYSIOLOGY  chap. 

only,  the  possibility  of  hipolar  excitation  with  stronger  induction 
currents  is  indicated  by  these  experiments.  The  excitation  at 
the  kathode  must,  of  course,  be  regarded  as  a  closing,  that  at  the 
anode  as  an  opening,  excitation. 

We  have  already  seen  that  the  direction  of  current,  with 
true  longitudinal  passage  through  a  muscle  with  parallel  fibres, 
would  theoretically  have  no  effect  upon  the  consequences  of  stimula- 
tion, but  that  the  sartorius  in  this  very  respect  gives  a  varying 
reaction,  owing,  no  doubt,  fundamentally  to  its  asymmetrical 
structure,  and  the  consequent  difference  in  current  density  at 
either  end.  On  careful  gradation  of  current  intensity  with  the 
rheochord,  it  may  be  seen  in  every  case  that  the  closure  of  the 
descending  current  regularly  produces  the  first  excitation  in  the 
longitudinally  traversed  sartorius  ;  it  is  only  with  greater  intensity 
of  current  that  the  closure  of  the  ascending  current  also  becomes 
effective ;  a  more  or  less  evident  difference  in  favour  of  the 
downward  direction  of  current  is  still  noticeable  in  many  cases. 
As  a  rule,  however,  this  difference,  which  is  at  first  conspicuous, 
grows  less  and  less,  until  at  last  with  stronger  currents  it  becomes 
imperceptible.  The  opposite  effect  occurs  with  the  break  excita- 
tion, to  which  the  ascending  direction  of  current  is  favourable. 
The  point  of  the  greatest  density  of  current  is  found  on  sending 
current  longitudinally  through  the  sartorius  at  the  lower  end  of 
the  muscle,  and  corresponds  with  descending  direction  of  current 
to  the  point  at  which  it  leaves,  with  ascending  current  to 
the  point  at  which  it  enters,  the  muscle-substance.  Since  in  the 
former  case  the  closure  twitch,  in  others  the  opening  twitch, 
appear  earliest,  these  facts  alone  show  the  probability — though 
only  for  currents  of  not  too  great  intensity — that  the  closing 
excitation  ^proceeds  from  the  kathode,  the  opening  excitation  from  the 
anode  (24). 

Again,  with  respect  to  the  duration  of  the  latent  period,  the 
difference  in  density  at  the  two  ends  of  the  longitudinally 
traversed  sartorius  is  very  conspicuous.  This  is  as  true  of  the 
make  as  of  the  break  excitation,  the  latent  period  being  in  fact 
invariably  shorter  when  the  excitation  starts  at  the  lower  (knee) 
end  of  the  muscle,  provided  the  strength  of  current  in  both  cases 
is  uniform  (Fig.  87,  a,  b).  Tigerstedt  subsequently  obtained 
the  same  results  (2,  p.  185  ff) 

In  view  of  the  fundamental  importance  of  the  law  of  polar 


ELECTRICAL  EXCITATION  OF  MUSCLE 


217 


excitation,  it  is  desirable  to  bring  forward  as  much,  and  as  well- 
substantiated,  experimental  evidence  as  possible  in  its  favour. 
Although  the  results  already  quoted  might  seem  to  be  sufficient 
proof,  the  reaction  of  partially  injured  onuscle  to  the  passage  of 
an  electrical  current  is  of  special  interest,  since  it  not  only  affords 
a  direct  proof  of  polar  excitation  in  v.  Bezold's  sense,  but  is  also 
of  great  moment  in  the  theoretical  action  of  the  current. 

If  the  sartorius  of  a  deeply-curarised  frog  is  exposed  as  care- 


lOAAAAAAAAAAAAA/VWVVVVAAAAAAAAAAAA 


Fig.  87. — a,  Closure,  contraction,  ascending  direction  of  current  (the  kathode  lies  at  the  pelvic 
end  of  the  sartorius).  The  lower  line  corresponds  with  the  kathodic  half.  6,  Closure  con- 
traction, descending  current.  The  upper  line  corresponds  with  the  kathodic  half  of  the 
muscle. 

fully  as  possible,  and  stretched  in  Hering's  double  myograph,  the 
make  excitation — which  previously  appeared  in  approximately 
equal  proportions  with  either  direction  of  current — will,  when 
one  end  of  the  muscle  is  crushed  by  forceps,  be  altogether 
abolished  or  considerably  weakened,  while  the  effect  of  the  closing 
excitation,  if  current  is  reversed  so  that  the  kathode  falls  on  the 
uninjured  end  of  the  muscle,  remains  unaltered.  The  break 
excitation  seldom  comes  about  even  after  long-protracted  passage 
of  current,  if  the  anode  is  on  the  injured  side  (26)  (Fig.  88), 


218 


ELECTRO-PHYSIOLOGY 


The  effect  of  partial  destruction  hy  heat  is  much  more 
pronounced  than  that  of  mechanical  injury,  since  after  the 
application  of  a  "  thermic  transverse  section "  the  excitability  of 
the  muscle  to  currents  of  medium  intensity  is  in  every  case 
entirely,  or  almost  entirely,  abolished,  when  the  effective  electrode 
happens  to  be  at  the  end  that  is  in  heat-rigor.  Since  both 
mechanical  injury  and  thermic  destruction  produce  a  swelling  of 
the  end  of  the  muscle,  as  well  as  other  disturbances  of  the  regular 
processes  of  the  fibres,  it  is  desirable  to  employ  a  method  which 


A  [' 


]'" 


B 


Fig.  8S.— Twitch  curve  of  sartorius  fixed  in  the  middle  and  stretched  in  the  double  myograph. 
(D"=under,  0  =  upper  half  of  the  muscle.)  Effect  of  injury  (death)  of  one  (the  lower)  end  of 
the  muscle.    The  pair  of  twitches,  A,  were  recorded  before,  B,  after  injury. 


will  kill  the  muscle,  while  avoiding  these  injuries  as  far  as 
possible.  Such  is  local  freezing,  according  to  Kiihne's  method,  in 
which  the  form  of  the  muscle -end  scarcely  alters  perceptibly. 
If,  in  addition  to  this,  the  muscle  is  immersed  in  some  indifferent 
fluid  traversed  by  parallel  lines  of  current,  the  methods  of  Engel- 
mann  (22)  and  Bernstein  (16)  will  be  still  more  exactly  carried 
out  in  this  experiment,  since  the  effect  of  the  asymmetrical  form 
of  the  muscle  is  here  totally  excluded. 

The  preceding  experiments  of  time  measurement  prove  that 
induced  currents  have  the  same  effect  upon  striated  muscles  as 
constant  currents  of  very  short   duration,  and  accordingly  that 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  219 

the  process  of  excitation  is,  as  a  rule,  discharged  only  at  the 
kathode.  If  it  is  further  remembered  that  the  break  shock 
excites  less  strongly  than  the  make  shock,  it  is  easy  to  compre- 
hend the  sequence  of  phenomena  which  are  observed  when  a 
curarised  sartorius  is  stimulated  with  gradually-increasing  make 
and  break  shocks,  sent  in  throughout  the  length  of  the  muscle. 

It  was  shown  above  that  the  difference  in  current  density, 
due  to  the  form  of  the  muscle,  at  the  points  at  which  the  current 
leaves  and  enters,  occasions  the  dissimilar  effects  of  excitation  in 
the  descending  and  ascending  constant  currents  :  this  is  equally  the 
case  with  the  induced  current,  so  that  the  polar  action  of  the 
latter  may  be  taken  as  proven.  The  experiment  is  even  more 
convincing  with  muscles  that  have  been  injured  at  one  end. 
Both  make  and  break  induction  currents,  sufficient  in  intensity  to 
produce  maximal  excitation  in  the  uninjured  sartorius,  when  the 
kathode  lies  at  the  end  nearest  the  tibia,  first  produce  excitation 
after  mechanical,  thermic,  or  chemical  destruction  of  the  latter, 
when  the  intensity  of  current  has  been  strengthened  by  pushing 
the  coil  up  considerably  further  (26).  If  the  injury  of  a  muscle 
with  parallel  fibres  is  not  confined  to  one  end,  but  both  are 
destroyed,  excitation  fails  with  both  ascending  and  descending 
direction  of  current,  so  that  a  muscle-fibre  bounded  by  two 
artificial  cross-sections,  traversed  in  its  total  extension  by  parallel 
lines  of  current  of  equal  density,  remains  unexcited  whether  the 
current  axis  is  parallel  with,  or  at  right  angles  to,  the  axis  of  the 
fibres.  Under  certain  conditions,  when  there  is  any  opportunity 
for  the  arising  of  effective  longitudinal  components,  excitation 
will  occur  sooner  than  it  does  with  pure  longitudinal  currents. 
With  the  aid  of  the  method  of  sending  current  transversely 
through  the  muscle  described  above,  these  facts  may  easily  be 
verified,  and  serve  to  explain  the  frequent  statement  that  the 
transverse  excitability  of  muscle  is  less  than  its  longitudinal 
excitability.  This  applies  in  particular  to  Giuffre's  experiments,  in 
which  bits  of  muscle  were  employed  bounded  on  both  sides  by  an 
artificial  cross-section. 

In  interpreting  the  peculiar  effect  exerted  by  local  injury 
(death)  of  the  ends  of  the  fibres  upon  the  excitability  of 
the  muscle,  with  longitudinal  passage  of  current,  it  is  very 
significant  that  total  death  of  the  fibre-ends  is  not  essential, 
certain    chemical  changes    of    the    muscle  -  substance    being    all 


220  ELECTRO-PHYSIOLOGY 


that  is  required  to  produce  these  conspicuous  manifestations 
of  electrical  excitation.  Most  of  the  salts  of  potassium  are 
known  to  be  acute  muscle  poisons,  since  when  introduced  in 
bulk  into  the  circulation,  or  applied  locally,  they  exercise  a 
highly  depressant,  or  inhibitory,  action  upon  the  excitability  of 
striated  skeletal  and  cardiac  muscle ;  many  acids  are  hardly  less 
inimical  to  muscle-substance,  even  when  highly  diluted.  It  is 
easy  to  demonstrate  that  local  treatment  of  one  or  the  other  end 
of  the  sartorius  with  these  substances,  which  are  inimical  to 
excitability  at  the  point  of  application,  produces  a  reaction  of 
the  muscle  to  current  analogous  to  that  with  localised  death  of 
the  fibres.  The  method  of  experiment  is  the  same  as  above. 
The  chemical  substances  to  be  investigated  are  diluted  in  various 
degrees  by  moistening  the  thin  (knee)  end  of  the  sartorius  with 
a  pad  of  cotton-wool  soaked  in  the  fluid  required,  or  by  dipping 
the  vertically  dependent  muscle  into  it.  The  effects  are  most 
striking  with  the  application  of  highly  dilute  (1  —  2  ^) 
solutions  of  acid  potassium  phosphate,  or  a  solution  of  meat- 
juice  saturated  with  the  same.  After  five  to  ten  minutes'  per- 
sistent action  on  the  tibial  end  of  the  muscle,  the  excitability 
to  closure  of  the  descending,  and  opening  of  the  ascending, 
current  is  invariably  more  or  less  diminished,  so  that  the  mani- 
festations of  contraction  fail  altogether,  or  are  conspicuously 
lessened,  if  the  effective  electrode  is  situated  at  the  end  of  the 
muscle  that  is  undergoing  chemical  alteration  (26).  It  must  be 
remarked  that  here,  as  in  the  previous  experiments,  it  is  not 
complete  abolition,  but  only  diminution,  of  excitability  to  one 
direction  of  the  current,  caused  by  local  "fatigue,"  that  ensues, 
so  that  strong  descending  currents  will  still  excite  a  sartorius 
treated  as  above,  although  no  perceptible  movement  of  the  muscle 
responds  to  the  impact  of  a  weaker  descending  current,  even 
when  its  intensity  is  quite  adequate  to  produce  a  maximal 
closure  excitation  in  an  ascending  direction. 

From  these  results  we  must  conclude  that  in  all  the  above 
cases  it  depends  not  so  onuch  upon  the  actual  death  of  the  contractile 
substance  in  any  localised  spot,  as  upon  the  consequences  of  chemical 
alteration  in  the  same,  ivhether,  and  to  tvhat  degree,  the  closing  and 
opening  excitation  become  effective  at  the  point  of  stimidation ;  and 
this  is  forced  upon  us  still  more  by  the  fact  that  with  local 
application  of  dilute  solutions  of  salts  of  potassium,  the  normal 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  221 

excitability  to  both  directions  of  current  is  completely  recovered 
after    washing    with    0'6    °/    ISTaCl    solution    in   a    short    time 

O  /O 

(10—15  minutes).  It  need  hardly  be  said  that  this  is  as  im- 
possible after  the  apphcation  of  substances  which  produce  deep- 
seated  chemical  and  physical  changes  in  the  contractile  substances, 
e.rj.  sublimates,  strong  acids,  alcohol,  etc.,  as  after  mechanical  or 
thermic  destruction  (26). 

The  corresponding  sodium  salts,  which  are  in  such  close 
chemical  relation  with  the  salts  of  potash,  exhibit  a  striking 
antagonism  in  their  physiological  effect  upon  striated  muscle. 
We  have  already  seen  that  the  excitabihty  of  certain  contractile 
substances  (spermatic  filaments,  ciliated  cells)  is  considerably 
heightened  by  ISTaoCOg  in  dilute  solutions,  and  in  discussing  the 
possibility  of  rhythmical  excitation  of  striated  muscle  by  the 
constant  current  it  was  pointed  out  that  the  effect  was  accentuated 
in  a  marked  degree  when  the  excitability  of  the  Jcathodic  end  of 
the  muscle  was  increased  by  treatment  with  ISTaaCOg.  If  the 
pelvic  end  of  an  uninjured  curarised  sartorius  dips  into  a 
0'5  —  1  %  solution  of  this  salt,  the  excitability  of  the 
muscle  to  the  closure  of  weak  ascending  currents  is  seen  after 
a  short  time  to  be  extraordmarily  augmented,  while  the  descend- 
ing current  still  works  quite  normally,  although  break  excitations 
are  discharged  with  such  low  intensity  of  current  and  brief 
duration  of  closure,  as  would  not  occur  in  a  normal  muscle  (26) 
(Fig.  89). 

Sometimes  under  these  circumstances,  with  weak  descending 
currents,  the  opening  twitch  is  conspicuously  delayed,  so  that 
the  tolerably  long  latent  period  of  the  opening  excitation  may 
be  observed  directly  without  further  artificial  aid.  Later  on  we 
shall  encounter  an  analogous  effect  in  the  indirect  excitation  of 
muscle.  The  significance  of  these  facts  to  the  theory  of  current- 
action,  and  the  law  of  polar  excitation  in  particular,  is  as  clear 
as  possible,  and  can  hardly  require  further  exposition.  They 
afford  as  direct  and  salient  a  proof  that  the  electrical  excitation 
of  the  muscle  is  a  i^olar  effect  of  current,  as  the  previous  experi- 
ments in  time  measurement ;  for  if  all  the  cross-sections  of  the 
intrapolar  tract  were  simultaneously  excited  there  could  never 
be  such  an  extraordinary  disparity  in  the  excitatory  action  of  the 
two  directions  of  current  as  is  exhibited  when  a  sartorius  muscle 
that   has    been    injured    at    one   end,    or    chemically   altered,   is 


222 


ELECTRO-PHYSIOLOGY 


traversed  in  its  entire  length  by  the  current.  We  saw  that 
excitation  only  remained  unaltered  when  the  effective  elec- 
trode was  at  the  uninjured  end  of  the  muscle ;  in  other  cases 
it  can  be  altered  in  a  positive  or  negative  sense  when  excitability 
is  locally  increased  or  diminished.  If  the  electrical  excitation 
of  a  muscle  is  once  admitted  to  be  a  'polar  eiiect  of  current,  it 
cannot  be  doubted  that  the  magnitude  of  both  closing  and 
opening  excitation  must  increase  or  diminish,  as  the  excitability 


Fig.  S9.— Twitch  curve  of  sartorius  fixed  from  the  centre  in  double  myograph,  a,  b,  Nonnal ; 
c,  d,  after  treatment  of  one  end  with  NaoCls  (upper  end  of  the  muscle).  Enormous  increase 
of  the  ascending  closure  twitch  ;  opening  twitch  with  weak  descending  currents. 

of  the  contractile  substance  at  the  points  where  current  enters 
or  leaves  the  muscle,  increases  or  diminishes.  Whether  excita- 
bility remains  unaltered  in  all  further  sections  of  the  muscle,  or 
whether  it  alters  in  a  negative  or  positive  direction,  is  undoubtedly 
of  great  moment  in  the  transmission  of  the  excitatory  process 
from  its  origin,  but  has  not  the  remotest  influence  upon  the 
intensity  of  the  excitatory  process  discharged  from  kathode  or 
anode.  We  may  conceive  a  muscle  with  parallel  fibres  of  equal 
diameter    at    both   ends,   having    its   cross  -  sections   collectively 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  223 

normal,  and  highly  excitable,  with  the  sole  exception  of  the 
ends  of  the  fibres  on  one  side,  at  the  point  at  which 
excitability  of  the  contractile  substance  has  been  artificially 
lowered  by  any  reagent ;  we  should  then  be  theoretically  justified 
in  the  expectation  that  on  sending  current  longitudinally  through 
such  a  muscle,  the  effects  of  the  closing,  as  of  the  opening, 
stimulus,  would  in  a  marked  degree  be  found  to  depend  upon  the 
direction  of  the  current,  since  the  same  stimulus  would,  in  the 
one  case,  act  upon  normally  excitable,  in  the  other  upon 
"  fatigued,"  substance.  In  proportion  as  the  local  depression 
of  excitability  is  higher  at  one  end  of  the  muscle,  the  more 
plainly  would  the  difference  in  the  excitatory  action  of  the  two 
directions  of  current  come  into  evidence.  And  further,  the 
extension  of  "  local  fatigue "  cannot  fail  to  affect  the  conse- 
quences of  excitation,  as  appears  from  the  following  considera- 
tion. If  we  picture  the  muscle  as  divided  into  zones  of  equal 
magnitude,  and  assume  that  excitability  is  depressed  in  the  end- 
zone  only,  while  it  remains  normal  in  the  others,  it  must 
obviously  be  possible  to  find  a  stimulus  of  the  right  strength 
to  discharge  an  excitatory  process  in  the  former,  which  will 
propagate  itself  by  conduction,  and  thus  bring  about  a  perceptible 
change  of  form,  either  in  the  entire  muscle,  or  at  least  in  the 
proximal  half  of  it.  But  the  same  minimal  stimulus  will  fail 
to  produce  this  effect  if  the  excitability  of  the  zones  immediately 
adjacent  to  the  terminal  section  is  depressed  in  the  same  pro- 
portion. For  in  such  a  case  the  excitation,  starting  with  the 
same  strength  as  before,  dies  out  within  a  very  short  area,  or 
gives  rise  to  a  weak  persistent  contraction  only. 

Such  a  muscle  as  we  have  been  imagining  can,  in  fact,  be 
produced  artificially.  With  careful  exposure  it  results  from 
treatment  of  one  or  other  end  of  the  sartorius  with  weak  solu- 
tions of  certain  salts  {e.g.  acid  potassium  phosphate,  and  meat- 
juice,  the  effect  of  which  is  probably  due  to  these  salts),  which  do 
not  essentially  alter  the  structure  of  the  immersed  section  of  the 
muscle,  but  partially  depress  its  excitability,  giving  the  oppor- 
tunity of  determining  the  correspondence  between  experimental 
data  and  theoretical  conclusions. 

But  the  electrical  current  itself,  by  repeated  closure  with 
unaltered  direction  of  current,  induces  still  more  completely 
a    condition    of    the    nmscle,   in    which    it   reacts    only   in    one. 


224  ELECTRO-PHYSIOLOGY 


and  that  the  opposed,  direction  of  current  to  the  closure  excita- 
tion, no  external  changes  being  perceptible.  It  can  scarcely 
be  doubted  that  this  state  also  must  be  interpreted  by  local 
fatigue  confined  to  the  point  at  which  current  leaves  the  con- 
tractile substance,  since  there  is  no  reason  for  assuming  alterations 
of  excitability  in  the  intrapolar  tracts,  either  positive  or  negative  ; 
while,  on  the  other  hand,  it  is  indubitable  that  the  excitatory 
process  at  the  ("  physiological ")  kathode  occurs  not  merely  at 
the  moment  of  closure,  but  is  also  continuous,  although  as  a 
diminishing  quantity,  during  the  entire  passage  of  the  current.  It 
must  therefore  be  taken  as  proven,  that  at  least  those  tracts 
of  the  muscle,  over  which  the  persistent  closure  excitation  extends, 
are  more  fatigued  than  the  rest  of  the  muscle,  in  which  no 
manifestations  of  excitation  can  be  detected  during  longer  passage 
of  not  excessively  strong  currents. 

The  difference  between  local  and  general  fatigue  of  a  muscle 
is  very  pronounced  when  the  response  of  a  muscle  fatigued  by 
tetanus  is  compared  with  that  of  one  that  has  been  polarised  by 
the  constant  current.  Uniform  stimuli  (single  induction  shocks 
are  best),  whose  efficacy  for  the  normal  muscle  has  been  tested, 
are  sent  into  different  points,  and  the  difference  in  height  of 
twitch  before  and  after  fatigue  determined.  In  the  first  case  the 
excitability  of  the  entire  muscle  will  be  much  diminished,  and 
entirely  abolished  for  weaker  stimuli  (that  had  previously  been 
effective),  while  a  polarised  muscle  reacts  to  stimuli  acting 
upon  its  continuity,  as  well  as  before  the  passage  of  the  current, 
although  the  closure  of  a  current,  in  the  same  direction  as 
the  "  polarising "  current,  produces  no  sign  of  contraction, 
when  it  happens  to  coincide  in  its  point  of  exit.  From 
this  we  may  conclude  that  the  cause  of  failure  of  excitation 
in  this  case  is  to  be  sought  in  alterations  localised  at  the 
point  at  which  the  current  leaves  the  muscle-substance,  or  in 
close  proximity  to  the  same.  This  also  appears  from  the  effects 
of  closing  a  current  opposed  in  direction  to  the  polarising  current, 
when  the  excitation  will  be  discharged  at  the  point  which 
was  formerly  the  seat  of  the  anode.  The  closure  twitch 
observed  under  these  conditions  in  the  polarised  muscle  is  con- 
siderably greater  than  before  the  passage  of  current  {voltaic  alterna- 
tive). If  this  is  correct,  the  effects  of  excitation  by  an  induction 
current  must  vary  according  as  it  is  sent  longitudinally  through 


ELECTRICAL  EXCITATION  OF  MUSCLE 


a  normal  muscle,  or  through  one  that  has  Ijeen  polarised,  care 
being  taken  in  either  case  that  the  points  at  which  the  current 
enters  or  leaves  the  muscle  are  not  altered.  For  since  it 
has  been  established  by  time -measurements  that  weak  induction 
shocks  set  up  an  excitatory  process  exclusively  at  the  kathode, 
we  may  advantageously  apply  this  fact  in  investigating  the  ex- 
citability of  the  kathodic  end  of  a  polarised  muscle,  by  stimulating 
it  through  its  entire  length. 

These  experiments  also  demonstrate  complete  uniformity  of 
response  in  a  sai"torius  of  which  one  end  has  been  brought  by 
the  action  of  certain  chemical  substances  into  a  condition  of 
depressed  excitability,  and  one  that  has  been  polarised  by 
continuous  passage  of  current  with  unaltered  direction ;  the 
preceding  discussion  can  be  referred  to  in  order  to  avoid 
repetition. 

In  conclusion,  it  should  be  remarked  that  the  manifestations 
of  fatigue  after  action  of  the  constant  current  are  usually 
the  same  as  after  injury  to  one  end  (heating  or  chemical 
destruction  of  a  muscle),  since  in  either  case  a  graduated 
diminution  in  magnitude  of  the  twitches  can  be  observed  before 
the  total  disappearance  of  the  closure  twitch,  while  the  persistent 
closure  contraction  continues  as  long  as  possible.  Little  doubt 
remains  therefore  that  the  local  depression  of  excitability — pro- 
duced in  the  one  case  by  the  resulting  continuous  excitation  at  the 
point  where  the  current  leaves  the  muscle,  in  the  other  by  a 
variously  expressed  chemical  alteration  of  the  muscle-substance — 
is  the  sole  cause  that  the  muscle  is  not  at  all,  or  very  little, 
excited  when  the  current  enters  or  leaves  it  by  the  end  thus 
affected,  while  in  other  cases  both  closing  and  opening  excitations 
follow  normally. 

The  following  facts  may  be  adduced  as  evidence  of  this 
proposition  :  in  a  preparation  of  sartorius  it  sometimes,  though 
seldom,  happens  that  the  fibres  remain  contracted  at  certain 
definite  points,  so  that  an  "  idio-muscular "  swelling  rises  up, 
now  in  the  middle,  and  now  at  one  or  the  other  end  of  the 
muscle.  The  first  case  is  the  most  frequent ;  whether  it  is 
connected  with  the  hyper-excitability  of  the  sartorius  at  the  point 
where  the  nerve  enters  it,  as  remarked  by  Kuhne,  must  remain  a 
moot  point.  When  the  swelling  is  confined  to  the  lower  end  of 
the  sartorius,  the  longitudinal  passage  of  the  current  expresses 

Q 


226  ELECTRO-PHYSIOLOGY 


itself  by  a  marked  reaction,  i.e.  only  the  ascending  current 
normally  discharges  the  make  excitation,  while  the  descending 
current,  which  is  usually  more  effective,  either  produces  no 
excitation  at  all  (with  medium  currents),  or  excites  in  a  much 
less,  degree  than  the  ascending  current.  Hermann  (28)  succeeded 
in  establishing  this  fact  of  "  polar  negative  action  "  at  the  idio- 
muscular  swelling  on  a  still  firmer  basis,  by  experiments  with 
cooled  muscle.  The  same  thing  occurs  where  all  trace  of  local 
contraction  has  already  died  out ;  for  the  latter  disappears  in 
some  cases  by  itself,  more  especially  when  the  muscle  is  immersed 
in  0'6  %  salt  solution.  Here,  as  in  the  persistent  closure 
contraction  due  to  the  constant  current,  a  state  of  depressed 
excitability  at  the  seat  of  the  idio-muscular  contraction  must 
have  intervened,  from  the  partial  continuous  excitation  consequent 
under  certain  conditions  upon  a  mechanical  excitation  (extension), 
which  is  indeed  a  necessary  consequence  of  the  fact  that  every 
excitation  is  accompanied  by  metabolism. 

We  have  already  mentioned  repeatedly  that  the  response  of 
a  sartorius,  of  which  one  end  has  been  killed  mechanically  or  by 
heating,  to  the  electrical  current,  can  be  satisfactorily  interpreted 
on  the  hypothesis  of  a  localised  diminution  of  excitability  at  the 
seat  of  stimulation,  and  we  have  now  to  examine  the  data  for  this 
conclusion. 

Since  it  is  a  well-substantiated  fact  that  an  uninjured  muscle, 
surrounded  on  all  sides  by  the  sarcolemma,  is  excited  each  time 
an  electrical  current  passes  out  at  any  point  of  its  surface,  and 
since,  further,  the  nature  of  the  conductor  by  which  the  entrance 
or  exit  of  the  current  is  effected  is  experimentally  indifferent— 
apart  from  the  unavoidable  polarisation  of  metal  electrodes — the 
response  of  a  muscle  injured  at  one  end  seems  at  first  sight  to 
be  an  exception  to  the  general  rule.  Here  we  find  that  both  the 
closing  and  opening  excitation  are  usually  wanting,  or  appear 
much  weakened,  when  the  current  passes  from  living  un- 
injured, into  dead,  muscle-substance,  or  vice  versd.  It  is  easy 
to  demonstrate  that  the  dead  contractile  substance  ^:)c?-  se  reacts 
to  current  like  any  other  animal  tissue  (tendon,  bone,  etc.)  that 
behaves  as  an  indifferent  conductor ;  the  clay  points  of  unpolaris- 
able  electrodes  can  be  covered  with  dead  muscle,  and  current 
led  through  them  to  the  uninjured  surface  of  a  muscle,  without 
causing  any  hindrance  or  difficulty  to  the  excitatory  process. 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  227 

There  must,  therefore,  in  the  continuity  of  a  muscle,  be  some 
specific  relation  at  the  limit  hetiveen  dead  and  living  fibres,  which 
is  capable  of  inhibiting  excitation. 

The  simple  experiment  of  reversal  of  current  proves  that 
the  total  excitahility  of  the  muscle  is  not  injured  by  destruction 
of  one  end,  but  there  is  reason  to  suppose  that  excitability 
in  the  immediate  proximity  of  an  injured  part  is  more  or  less 
diminished.  This  appears  indeed  to  be  contradicted  by  the 
experiment  of  bringing  the  epiphysis  of  the  tibia  (or  of  the 
pelvis,  if  the  upper  end  of  the  sartorius  is  injured)  into  relations 
of  conductivity  with  some  point  on  the  surface  of  the  muscle,  by 
means  of  a  bridge  of  salt  clay,  beyond  the  injured  part ;  the 
muscle  will  contract  almost  as  sharj^ly  at  closure  of  a  descending 
(or  ascending)  current  as  before  the  injury :  but  it  must  be 
remembered  that,  according  to  all  probabilities,  the  condition  of 
acute  depression  of  excitability  is  confined  to  the  immediate 
proximity  of  the  point  injured ;  at  all  events  this  must  occur 
immediately  after  the  ends  of  the  fibres  have  been  crushed  on  the 
one  side.  That  excitability  nmtst,  generally  speaking,  he  diminished- 
at  the  border  between  dead  and  living  fibres,  follows  from  the 
fact  that  the  process  of  dying  invades  the  entire  length  of  a  fibre 
continuously,  when  once  it  has  been  introduced  at  any  point ; 
accordingly  dead  and  living  fibres  are  never  in  immediate  juxta- 
position, but  the  section  of  the  muscle  that  has  been  structurally 
disturbed  by  the  attack,  and  killed,  must  in  the  adjacent  sections 
initiate  every  possible  process  of  dying,  and  correlative  state  of 
excitability,  as  has  already  been  pointed  out  by  Hermann.-^ 

If  it  is  true,  as  stated  above,  that  the  eoetension  of  "  local 
fatigue "  is  important  in  determining  whether  an  electrical 
stimulus  of  given  magnitude  does  .or  does  not  produce  change 
of  form  in  the  muscle,  we  may  presume  that  the  slow  dying 
of  one  or  the  other  end  of  the  sartorius,  on  immersion  in  warm 
water,  depresses  the  excitability  of  the  muscle  to  one  direction 
of  the  current  more  completely  than  simple  mechanical  injury : 
it  cannot  be  doubted  that  the  local,  slowly -increasing  effect  of  rising 
temperature  is  able  to  produce  complete  gradation  of  excitability 
in  the  sections  of  the  muscle  proximal  to  the  section  in  heat- 
rigor.      This  view  is  confirmed  experimentally  {supra). 

1  Hermann,    Weitcrc  Untcrs.  z.   Phys.  d.  Ncrvcn  u.   Ihiskcln.      Berlin,   1867, 
p.  5  f. 


228  ELECTRO-PHYSIOLOGY 


The  universal  validity  of  the  law  of  polar  excitation  being 
thus  unequivocally  established  in  the  case  of  striated  skeletal 
muscle,  there  is  a  'priori  no  doubt  of  its  further  applicability 
to  cardiac,  as  well  as  to  smooth,  muscle.  In  view  of  the  structure 
of  the  heart  (consisting,  like  all  other  smooth  muscle,  of  innumer- 
able cells  in  close  juxtaposition,  connected  together  \)j  cement- 
substance),  the  question  may  fairly  be  asked,  what  —  relatively 
to  the  previous  definition  —  must  here  be  understood  by  the 
"  physiological  anode  or  kathode  ? "  To  take  a  simple  case,  if  we 
imagine  a  strip  composed  of  parallel  fibre-cells,  as  is  approximately 
shown  in  a  preparation  of  molluscan  adductor  muscle,  we  may 
expect  such  a  preparation  when  traversed  longitudinally  by 
current  to  behave  like  a  polymerous,  cross-striated  muscle,  the 
several  parts  of  which  must  be  regarded  anatomically,  and 
physiologically,  as  independent  individuals.  This  is  well  exhibited 
in  the  M.  rectus  abdominis  of  the  frog.  If  current  is  sent 
through  this  muscle,  when  it  has  been  exposed  and  stretched 
between  two  corks,  there  is,  as  might  be  expected,  at  and  during 
closure,  on  the  anodic  side  of  each  tendinous  intersection  (if  ex- 
amined with  transmitted  light  under  the  magnifying  lens)  a  clear 
and  sharply-delimitated  swelling  of  the  ends  of  the  fibres  corre- 
sponding with  the  persistent  kathodic  closure  contraction.  It 
disappears  at  the  moment  of  breaking  the  circuit,  eventually 
making  way  for  persistent  anodic  opening  contraction  on  the 
other  side  of  the  intersection.  It  follows  of  course  that  the  closing 
and  opening  twitch  of  each  part  must  proceed  from  the  same 
point. 

The  whole  segmented  muscle-band  will  thus  be  excited  at  as 
many  points  in  its  continuity  as  it  has  divisions,  since  each 
element  of  the  muscle  circuit  has  its  kathode  and  anode  respect- 
ively. And  if  the  adjacent  cells  of  the  heart,  or  any  other 
smooth  muscle,  conduct  themselves  like  the  constituents  of  a 
polymerous  muscle,  and  if  the  interstitial,  or  cement,  substance 
plays  the  same  part  as  the  tendinous  intersection,  it  may  be  pre- 
sumed that  the  electrical  current  will  produce  excitation  at 
closure  (or  opening)  at  as  many  points  in  the  continuity  of  the 
tract  as  there  are  cells  present.  For  obviously  the  latter  would 
each  have  their  proper  kathode  and  anode,  so  that,  in  conse- 
quence of  the  inferior  length  of  the  cell  elements  in  question, 
the  excitation  (contraction)  would  in  fact  begin  simultaneously  at 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  229 

innumerable  points  of  the  whole  area  traversed.  Experimentally, 
however,  the  reaction  of  such  a  muscle,  constructed  of  uninuclear 
celb,  in  no  way  corresponds  with  this  theoretical  process.  We 
have  learned  from  Engehnann's  classical  experiments  that  the 
ureter,  like  the  heart,  conducts  itself  re  both  transmission 
of  the  excitatory  process,  and  polar  excitation  by  the  electrical 
current,  "  like  a  single,  gigantic,  hollow  muscle-fibre."  This  proves 
once  more  that  the  cement  substance  does  not  separate  the  cells 
by  forming  indifferent  partition  walls,  but  actually,  as  it  were, 
brings  about  the  continuity  of  the  substance.  A  series  of 
muscle-cells,  with  the  ends  abutting  on  each  other,  and  traversed 
longitudinally  by  current,  would  react  towards  it  as  a  single 
muscle-fibre,  and  the  connective  substance  would  no  more  form 
secondary  kathodes  and  anodes  than  the  transverse  discs  within 
the  striated  fibrils.  In  the  one  case,  as  in  the  other,  there  is 
2)hi/siological  continuity  of  substance.  This  can  be  proved  experi- 
mentally, both  in  cardiac,  and  in  various  instances  of  smooth, 
muscle.  If  the  ventricle,  separated  from  the  auricle,  of  the 
frog's  heart  (the  '"'  cardiac  apex  "),  is  used  as  the  object  of  experi- 
ment, the  asymmetrical  form  of  the  preparation  entails  the  same 
result  as  in  the  sartorius,  i.e.  the  density  of  current  on  direct 
application  of  the  electrodes  to  either  end  (apex  and  base)  is  very 
unequal.  It  is  therefore  advisable  to  immerse  the  apex,  accord- 
ing to  Engelmann's  method  (27,  p.  201),  in  an  excitation  chamber 
filled  with  indifierent  fluid,  so  that  there  is  approximately  equal 
current-density  at  every  point  of  the  preparation,  so  long  as  the 
cuiTent  is  passing.  Engehnann  employed  a  glass  vessel  13  cm. 
long,  -4  cm.  wide,  and  3  cm.  high,  filled  to  about  1-^-  cm.  with 
a  dilute  solution  of  XaCl  (0*5  /{)  and  gum  arable  (2  ^), 
which  the  electrodes  dipped  into.  On  closing  a  battery 
current,  or  sending  in  a  single  induction  shock,  it  is  found  that 
if  the  long  axis  of  the  ventricle  lies  parallel  with  the  lines  of 
current,  the  cut  surface  being  vertical  to  the  same,  ascending 
currents  {i.e.  from  apex  to  base)  fail  to  excite  immediately,  or 
soon  after  making  the  section,  or  at  least  excite  less  effectively 
than  descending  currents.  After  a  few  minutes,  however,  the 
excitabiLity  to  ascending  currents  reasserts  itself,  and  rapidly 
increases,  sinking  again  to  zero  if  the  section  is  freshened.  The 
same  dependence  of  excitation  effects  on  direction  of  current  ap- 
pears also  after  injurv  to  one  or  the  other  lateral  surface  of  the 


230  ELECTRO-PHYSIOLOGY 


preparation,  provided  it  is  so  arranged  that  the  cut  surface  is 
perpendicular  to  the  direction  of  current. 

For  the  sake  of  brevity,  we  may,  with  Hermann,  denote  the 
direction  of  the  exciting  current  which  lies  towards  the  cut 
surface  "  atterminal  "  ("  admortal  "),  the  other  as  "  abterminal  " 
("  ahnortal "),  The  reaction  observed  may  then  be  shortly 
expressed  as  follows  : — Immediately  after  injury  to  the  cardiac 
apex,  the  closure  of  atterminal  currents  is  ineffective,  while  tinder 
similar  conditions  the  closure  of  ahtcrminal  currents  is  excitcdory. 
Obviously  we  have  here  a  complete  analogy  to  the  response  of 
the  sartorius  of  which  one  end  has  been  injured  (or  otherwise 
chemically  altered),  and  the  same  conclusions  may  be  deduced  in 
both  cases.  In  the  first  place,  experiment  proves  convincingly  that 
the  contractions  of  the  heart  with  electrical  excitation  proceed 
exclusively  from  the  spot  where  the  current  passes  from  the  living 
muscular  tissue  into  the  foreign  medium  beyond  it,  whether  this  is 
salt  solution  or  dead  muscle-substance.  This  represents  the  physio- 
logical kathode  of  the  preparation,  and  here  alone  can  the  make 
excitation  originate.  On  this  presumption  only  does  the  effect 
of  local  injury  upon  excitability  to  closure  of  atterminal  currents, 
with  failure  of  effect  upon  excitability  to  abterminal  closure, 
become  intelligible.  It  holds  good,  however,  for  the  apex  of  the 
heart,  which  consists  of  innumerable  irregularly  fused  cells,  just 
as  much  as  for  the  approximately  parallel  -  fibred  monomerous 
sartorius. 

In  both  cases  the  excitation  propagates  itself  at  closure  over 
the  whole  surface  of  the  muscle,  from  its  point  of  departure,  by 
conductivity  (from  cell  to  cell),  the  exact  seat  of  the  kathode  on 
the  surface  of  the  preparation  seeming  to  be  quite  indifferent, 
while  the  excitability  of  the  points  affected  has,  on  the  other 
hand,  an  important  influence  on  the  consequences  of  excitation. 
If  the  current  leaves  by  an  injured  point,  excitation  takes  place 
at  a  less  excitable  spot,  and  the  effects  can  be  interpreted  just 
as  in  sartorius,  under  similar  conditions.  The  only  noticeable 
difference  is  the  rapid  restoration  of  normal  reactions.  Engel- 
mann  explains  this  naturally  by  the  assumption  that  the  single 
cells,  though  connected  by  relations  of  conductivity  with  their 
neighbours  while  living,  die  singly,  each  to  itself ;  in  other  words, 
the  process  of  dying  does  not  pass  over  from  cell  to  cell  like 
that  of  excitation.      Where  the  superficial  cells  are  quite  dead. 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  231 

the  kathode  no  longer  falls  at  the  limit  of  moribund,  i.e.  less 
excitable,  muscle -substance  on  the  one  hand,  and  surrounding 
fluid  or  dead  cell-substance  on  the  other,  but  lower  down  at  the 
border  of  living  and  dead  cells,  i.e.  at  the  demarcation  surface. 
Every  polynierous  striated  skeletal  muscle,  as  t3an  easily  be 
demonstrated,  exhibits  the  same  reaction.  The  consideration  of 
the  electromotive  action  of  the  heart  (infra)  further  confirms 
this  theory.  Another  method  of  demonstrating  the  law  of  polar 
excitation  on  cardiac  muscle,  when  it  is  totally  uninjured  and 
remains  in  diastolic  relaxation,  is  the  so-called  unipolar  stimula- 
tion. Since  excitation  by  the  electrical  current  depends  in  the 
first  place  upon  its  density  at  the  point  of  ingress  or  egress,  it  is 
prima  facie  evident  that  the  diminution  of  the  same  at  one  pole, 
with  simultaneous  maximal  increase  at  the  other,  may  furnish  an 
explanation  of  the  law  of  polar  current  action.  Thus,  indeed,  as 
was  pointed  out  by  Klihne  (28),  we  may  obtain  an  electrical 
excitation  as  weak  as  that  formerly  produced  by  mechanical 
excitation.  If  two  punctiform  leading-in  electrodes  are  imagined 
upon  the  surface  of  any  conductor,  the  whole  interior  of  the 
same  will  be  traversed  by.  lines  of  current,  whose  density  is 
greatest  at  the  point  of  contact,  and  slowly  diminishes  outwards. 
And  if  by  employing  a  flat  electrode,  the  density,  and  consequently 
the  efficacy,  of  the  current  is  rendered  minimal,  or  negative,  at 
the  point  where  it  enters,  or  leaves,  the  muscle,  the  other  elec- 
trode only  will  finally  remain  effective  at  the  point  of  contact,  and 
may,  as  it  were,  be  localised  by  limiting  the  surface  of  the  con- 
tact as  much  as  possible.  If,  for  example,  the  skin  is  removed 
from  the  ventral  surface  of  the  thig-h  of  a  curarised  frog, 
the  broad  surface  of  one  (the  indifferent)  electrode  being 
applied  to  the  skin  of  the  throat,  while  the  other,  the  finest 
possible  pencil  electrode,  is  in  contact  with  any  point  of  the 
moist  surface  of  the  muscle,  characteristic  effects  of  excitation 
appear,  which  differ  widely,  according  as  contact  is  effected  at  the 
kathode  or  anode.  In  the  first  case,  on  sending  in  a  weak 
current,  the  bundles  of  fibres  immediately  under  the  point  of  the 
electrode  may  be  seen  to  contract  at  the  moment  of  closing  the 
circuit,  producing  for  a  moment  a  small  longitudinal  furrow  on 
the  smooth,  even  surface  of  the  muscle,  while  at  the  actual  point 
at  which  contact  is  effected  a  small,  sharply-defined  transverse 
swelling  appears,   which — -provided   the   contact   is  unbroken — ■ 


232  ELECTEO-PHYSIOLOGY 


persists  unaltered  throughout  the  entire  period  of  closure.  We 
cannot  doubt  this  to  be  a  persistent  kathodic  closure-contraction. 
If  the  intensity  of  the  excitation  current  is  strengthened,  both  the 
twitch  and  the  continuous  contraction  increase  also,  although  the 
latter  never  loses  its  localised  character.  This  appears  most 
clearly  if  (as  above)  marks  are  affixed  to  the  surface  of  the 
muscle,  which,  by  moving  in  opposite  directions  during  contrac- 
tion, are  a  measure  of  its  spatial  extension.  The  muscle  investi- 
gated may,  e.g.,  be  painted  with  sepia  bands  at  right  angles  to  the 
direction  of  the  fibres,  so  that  the  distance  between  each  two 
lines,  drawn  with  a  fine  bristle,  is  about  ^  mm.  Every  contrac- 
tion thus  defined  expresses  itself  therefore  by  a  more  or  less 
conspicuous  decrease  in  one  or  several  cross -bands,  or  the 
uncoloured  spaces  between  them.  Within  those  tracts  of  the 
muscle,  on  the  other  hand,  which  are  only  passive  factors,  the 
coloured  cross-bands,  though  variously  distorted,  do  not  become 
smaller.  It  is  undeniable  that  with  the  unipolar  method  of 
excitation,  as  described  (where  the  lines  of  current  do  not,  gener- 
ally speaking,  pass  in  and  out  through  the  natural  ends  of  the 
muscle,  but  traverse  the  fibres  in  the  most  opposite  directions, 
oblique  and  tranverse, — which  must  partially  affect  the  current 
action),  the  conditions  of  experiment  are  less  easy  to  summarise 
than  with  the  customary  bipolar  method,  and  the  results, 
e.g.,  in  regard  to  the  possibility  of  action  from  secondary 
kathodic  or  anodic  points  in  the  proximity  of  the  exciting 
electrode,  often  hard  to  interpret.  Still  this  method  has  its 
advantages  in  many  cases  where  the  bipolar  method  could  not 
well  be  brought  into  application.  This  occurs  emphatically 
in  many  smooth  muscular  parts,  and  not  less  in  cardiac  muscle, 
where  the  complex  and  intricate  course  of  the  fibres  makes  it 
a  loriori  impossible  for  the  current  to  traverse  all  the  individual 
elements  longitudinally.  The  cells  thus  fitted  together  in  all 
conceivable  directions  would  more  probably  be  traversed  by  the 
lines  of  current  in  the  most  various  directions,  and  at  widely- 
divergent  angles.  But  as  shown  by  the  above,  this  is  of  little 
importance  to  the  final  consequence.  If  the  ventricle  of  the 
frog's  heart  is  arrested  in  diastole,  according  to  Bernstein's 
method,  by  squeezing  it  away  from  the  auricle,  it  appears  filled 
out  with  blood,  and  reacts  to  every  mechanical  stimulus  by 
a  powerful  total  contraction.       If,  once  more,  the  broad  electrode 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  233 

of  the  battery  current  is  applied  to  any  indifferent  part  of  the 
frog's  body,  while  the  other  is  in  contact  with  the  surface  of 
the  ventricle,  the  closure  of  the  circuit  will,  on  stimulating  with 
a  just  effective  current,  without  exception  excite  only  when 
contact  with  the  heart  is  made  by  the  kathode,  never  when  it  is 
formed  by  the  anode ;  sometimes,  however,  the  opening  (at  least 
after  a  long  closure)  will  also  be  effective.  And  if  the  validity 
of  the  polar  law  of  excitation  is  thus  incontestable  for  cardiac 
muscle,  it  can  be  demonstrated  in  appropriate  cases  for  smooth 
muscle  also. 

As  such,  we  may  refer,  inter  alia,  to  the  adductor  muscle  of 
Anodonta,  of  which  the  response  to  current  has  already  been  fre- 
quently quoted,  and  which,  from  its  generally-speaking  regular  and 
parallel-fibred  structure,  presents  the  best  comparison  with  the 
frog's  sartorius.  It  was  said  above  that  a  preparation  of  the 
adductor  muscle,  as  free  from  tonus  as  possible,  persists  in  a 
shortened  state  during  the  entire  passage  of  the  current.  The 
merest  inspection  will  suffice  to  show  that  neither  at  closure  nor 
opening  (where  the  latter  is  effective)  of  the  current  does  the 
entire  intrapolar  tract  become  persistently  and  uniformly  con- 
tracted, but  in  the  first  instance  the  kathodic,  in  the  second  the 
anodic,  half  will  be  mainly  affected.  Undoubtedly  this  is  a 
phenomenon  analogous  with  that  of  the  transversely  striated  frog's 
sartorius,  where  the  corresponding  localisation  of  the  closing,  or 
opening,  persistent  contraction  has  long  been  known,  and  has 
always  been  regarded  as  substantial  confirmation  of  the  law  of 
polar  excitation  by  the  electrical  current.  More  exact  conclu- 
sions are  obtained  from  the  application  of  the  graphic  method 
recording  the  separate  contraction  of  either  half  of  the  muscle, 
which  is  possible  here  as  in  the  sartorius,  by  fixing  the  centre  of 
the  muscle.  But  while  in  striated  muscle,  as  a  rule,  at  the 
moment  of  closure,  as  also  eventually  at  break  of  the  cur- 
rent, a  wave  of  contraction  is  propagated  from  the  kathode,  or 
anode,  with  great  velocity  through  the  entire  length  of  the 
muscle,  producing  on  either  side  of  the  fixed  centre  an  approxi- 
mately equal  twitch  at  closure  or  opening,  in  moUuscan  muscle 
we  find  only  a  more  or  less  localised  persistent  contraction, 
corresponding  with  the  persistent  closing  and  opening  contrac- 
tion of  striated  muscle,  which,  like  these,  fails  altogether  if  the 
entrance  or  exit  of  the  current  is  effected  by  a  layer  of  dead  con- 


234 


ELECTRO-PHYSIOLOGY 


tractile  substance  (3).  Of  this  the  accompanying  curve  (Fig.  90) 
gives  sufficient  evidence.  As  in  cardiac  muscle,  the  striking 
disparity  of  effect  between  the  two  directions  of  current  immedi- 
ately after  the  injury  equalises  itself  by  degrees,  and  at  last 
becomes  imperceptible.  The  explanation  here  again  must  be 
sought  in  the  independent  dying  of  each  fibre-cell. 

If  these  conclusions  from  the  adductor  muscle  of  Anodonta 
are  in  almost  complete  conformity  with  the  polar  effects  of  current 
in  striated  skeletal  and  cardiac  muscle,  this  is  not  equally  true  of 
other  parts  composed  of  smooth  fusiform  cells,  in  which  excita- 
tion with  the  constant  current  provokes  a  series  of  manifestations 
differing  in  many  respects  (at  least  at  first  sight)  very  widely, 


Fig.  90. — Localisation  of  persistent  closure  contraction  at  the  kathode  (/v)  on  exciting  the 
adductor  muscle  of  Anodonta.   S  =  closure  ;  0  =  opening. 


and  thus  suggesting  that  the  polar  law  of  excitation  may  not  be 
rigidly  applicable  to  all  kinds  of  muscle  (31). 

Within  the  integument  of  Holothuria,  along  the  entire  length 
of  the  body,  there  is  a  beautiful  series  of  longitudinal  muscle- 
bundles,  with  parallel  fibres,  in  the  form  of  five  flat  bands,  com- 
posed of  solitary  spindle-cells,  pointed  at  either  end,  which,  after 
the  animal  {R.  Poli)  is  opened,  appear  as  pale,  or  pinkish,  and 
transparent  striee.  Many  thinner  and  finer  bands  of  circular 
muscle  run  between  each  two  longitudinal  muscle-bands,  form- 
ing a  complete  investment  of  the  body  at  right  angles  to  the 
latter,  and,  like  them,  consisting  of  spindle-cells.  In  the  muscu- 
lar integument,  when  split  up  lengthways,  and  properly  stretched, 
the  longitudinal  muscle -bands  may  easily  be  isolated  in  their 
whole  length,  or  in  portions  only,  by  passing  a  probe  under  one 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  235 

end  of  the  muscle  and  pushing  it  along  the  muscular  band, 
pressing  it  against  the  attachment.  Excitation  experiments  can 
then  be  tested  on  this  isolated  and  freely -stretched  band  of 
muscle,  just  as  in  the  muscle  of  Mollusca.  In  every  instance 
the  protracted  tonic  contraction  into  which  these  muscles 
usually  fall,  more  especially  after  mechanical  injury,  is  very 
disturbing ;  but  after  a  period  of  rest  under  sea-water  relaxation 
sets  in  again  sufficiently  to  make  experiment  possible ;  a  certain 
degree  of  tonus,  however,  persists  and  must  be  taken  into  considera- 
tion. If  two  fine  pencil  electrodes  are  then  applied  simultane- 
ously to  two  points,  not  too  close  together,  of  a  longitudinal 
muscle-band,  lying  in  situ  or  stretched  between  two  corks,  or  if 
one  electrode  is  laid  on  some  indifferent  part  of  the  preparation, 
the  other  only  being  in  contact  with  the  muscle,  there  will,  in 
either  case,  be  characteristic  changes  of  form  at  the  points  where 
current  enters  or  leaves  the  muscle,  differing  widely  at  the  two 
poles  (29). 

As  soon  as  the  circuit  is  closed,  a  small  transverse  swelling 
arises  at  the  kathode,  exactly  under  the  electrode  in  contact,  and 
extends  thence  at  right  angles  to  the  direction  of  the  fibres ; 
under  some  conditions  (not  too  weak  a  current)  this  swelling 
spreads  over  the  whole  breadth  of  the  muscle-band,  and  stands 
out  sharply  from  the  region  round  it.  This  "  idio-muscular," 
kathodic  swelling  persists  during  the  period  of  closure,  and  (what 
is  specially  remarkable)  never  spreads  beyond  the  point  where  it 
originates.  The  total  shortening  of  the  muscle-band  produced  by 
the  localised  contraction  is  always  insignificant,  since  it  is  essen- 
tially only  the  part  of  the  muscle  immediately  adjacent  to  the 
exciting  electrode  which  contributes  to  the  local  expansion.  It 
also  depends,  of  course,  upon  the  strength  of  the  current  used  for 
excitation,  so  that  within  a  certain  range  the  kathodic  swelling, 
which  undoubtedly  corresponds  with  the  persistent  closure  con- 
traction of  striated  muscle,  increases  with  the  strength  of  the 
current,  and  then  includes  a  larger  tract  of  the  muscle.  With 
very  weak  minimal  currents  the  upper  layers  of  fibres  only  con- 
tract locally,  so  that  the  kathodic  swelling  does  not  extend  over 
the  whole  thickness  of  the  muscle.  In  all  cases  the  sharp  delimit- 
ation of  the  kathodic  continuous  contraction  is  very  remarkable, 
— it  rises  in  a  crest,  descending  sharply  on  both  sides  to  the 
surface  of  the  muscle. 


236  ELECTRO-PHYSIOLOGY 


The  excitation  effects  produced  under  similar  conditions  at 
the  point  where  the  current  enters  are  quite  different.  Here  at 
the  point  where  the  anodic  electrode  is  in  contact  with  the  smooth, 
even  surface  of  the  muscle,  a  more  or  less  profound  canal  or  furrow 
arises  at  make  of  the  current,  and  runs  transversely  over  the 
muscle ;  its  length  and  breadth  correspond  more  or  less  with 
the  transverse  swelling,  which  appears,  or  (with  unipolar  excita- 
tion) would  have  appeared,  under  the  same  conditions  at  the 
kathode.  It  is  easy  to  see  that  the  bulk  of  the  muscle  is  pushed 
over  from  the  anodic  side  at  the  moment  of  closure,  and,  as  it 
were,  flows  away,  while  on  either  side  of  the  hollowed  canal  a 
swelling  rises  up,  of  similar  aspect  to  the  kathodic  continuous 
contraction.  The  changes  of  form  in  the  muscle  which  ensue 
may  therefore  be  characterised  as  a  deep  hollow,  rising  up  under 
the  electrode,  marked  off  on  either  side  by  a  transverse  swelling. 

Under  certain  conditions  yet  to  be  considered,  it  appears  as 
though  the  two  swellings  were  formed  solely  from  the  muscle - 
substance  dragged  away  from  the  anode.  But  if  the  experiment 
is  made  with  fresh,  excitable  preparations,  it  will  be  found,  with- 
out exception,  that  a  conspicuous  contraction  appears  on  both  sides 
of  the  anode,  and  extends  over  comparatively  wide  tracts  of  the 
muscle ;  it  is  most  evident  in  the  immediate  proximity  of  the 
hollowed  canal,  and  decreases  on  both  sides  of  it.  In  other 
words,  at  make  of  the  current  the  muscle  elongates  itself  close  to 
the  anode  by  relaxing,  while  in  consequence  of  the  excitation 
produced  in  the  surrounding  region,  the  muscle-substance  presses 
in  towards  the  relaxed  point.  In  this  way  there  is  often  for  the 
whole  muscle  a  more  considerable,  and  always  much  more  im- 
portant, shortening,  than  in  kathodic  excitation. 

Since  the  flat  longitudinal  muscle-bands  of  Holothuria  are 
tolerably  broad,  the  excitation  effects  described  above  can  only 
appear  in  one  part  of  the  fibres,  when  the  electrode  points  are 
applied  to  the  centre  of  the  muscle.  The  changes  of  form  are, 
however,  much  more  striking,  and  can  be  seen  at  a  greater  dis- 
tance, if  the  muscle  is  lightly  stroked  with  the  brush  electrode  at 
right  angles  to  the  direction  of  the  fibres. 

The  same  manifestations  (as  on  the  electrical  excitation  of 
the  longitudinal  muscle-bands)  appear  in  the  thin  bundles  of  the 
circular  muscles,  although  they  are  less  striking  owing  to  the 
greater  delicacy  of  structure.     If  a  perfectly  level  point  of  the 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  237 

surface  is  13rouo'ht  into  contact  with  the  kathode,  a  small  longi- 
tudiual  swelling  springs  up  under  the  point  of  the  electrode  as 
soon  as  the  current  is  made,  its  long  axis  lying  perpendicular 
with  the  course  of  fibres  in  the  muscular  bundle  excited.  The 
wdiole  manifestation  is  indisputably  the  same,  in  a  less  degree,  as 
the  persistent  kathodic  contraction  when  a  longitudinal  muscle- 
band  is  excited. 

In  both  cases  there  is  the  striking  demarcation  of  the  swell- 
ing, as  well  as  the  inconspicuous  total  contraction  of  the  muscle, 
due  to  local  excitation.  In  contrast  with  this,  the  total  contrac- 
tion of  the  ring-muscles  is  very  marked  with  unipolar  stimulation 
from  the  anode.  Careful  gradation  of  current  and  a  fine-pointed 
brush  electrode  are  essential  in  order  fully  to  determine  the  con- 
trast of  excitation  effects  in  circular  and  longitudinal  muscles  in 
this  case  also.  If  a  single  bundle  of  circular  fibres  is  excited  in 
the  middle,  between  two  longitudinal  muscle-bands,  the  most 
striking  appearance  on  closing  the  current  is  the  formation  of  a 
furrow  running  parallel  with  the  direction  of  the  fibres,  the 
origin  of  w^hich  is  easy  to  explain  from  the  sharp  contraction  of 
the  excited  fibres.  With  artificial  enlargement,  it  is  easy  to  see 
that  the  muscle-fibres  immediately  under  the  point  of  the  anode 
do  not  take  part  in  the  contraction,  but  (as  in  longitudinal 
muscle  under  corresponding  conditions),  a  more  or  less  well- 
marked  canal  is  formed,  running  transversely  to  the  fibres,  at 
either  side  of  which  the  muscle-bundle  shortens.  Sometimes 
the  transverse  swellings  which  mark  off  the  canal  on  either  side 
stand  out  quite  clearly ;  yet  it  always  requires  close  observation 
to  detect  an  appearance,  which  is  obvious  when  the  longitudinal 
muscles  are  excited.  While  in  the  latter,  with  anodic  excitation, 
total  contraction  tends  to  disappear  in  favour  of  local  changes  of 
form  owing  to  the  great  length  of  the  muscle-bands,  the  exact 
opposite  occurs  in  the  small  short  bundles  of  circular  fibres,  in 
which  the  total  effect  is  more  striking  than  the  local  changes. 
This  is  best  studied  at  points  where,  from  the  contraction  of  the 
surrounding  parts  and  consequent  folding  over  of  the  membrane, 
or  from  pronounced  total  relaxation,  individual  parts  stand  out 
in  a  blister.  If  contact  is  made  with  the  anode  at  such  a 
part,  where  the  circular  fibres  appear  curved  convexly  outw^ards, 
closure  at  once  produces  a  segmental  constriction,  parallel  with 
the  fibres,  and  recalling  the  similar  effect  produced  under  analogous 


238  ELECTRO-PHYSIOLOGY 


conditions  in  the  intestine,  more  particularly  in  the  colon  of 
Herbivora.  This,  however,  obviously  makes  any  exact  investiga- 
tion of  the  local  changes  arising  at  the  point  of  contact  itself  as 
good  as  impossible.  With  kathodic  stimulation,  on  the  contrary, 
they  are  very  apparent,  inasmuch  as  a  small,  but  sharply-de- 
fined, transverse  swelling  is  formed,  with  only  minimal  total 
shortening  at  the  point  where  the  current  leaves  the  muscle. 

The  smooth  masticatory  muscles  of  Echinus  esculentus  exhibit 
a  no  less  remarkable  and  characteristic  response  to  electrical 
excitation  with  the  galvanic  current,  the  reactions,  moreover, 
being  much  more  rapid  than  in  Holothurian  muscle  (29).  The 
calcareous  skeleton  of  the  so-called  lantern  of  Aristotle  consists 
of  five  symmetrical  segments,  each  again  consisting  of  several 
pieces.  The  segments  are  joined  together  partly  by  bands, 
partly  by  very  strong  muscles,  which  are  partially  very 
regular  in  structure.  This  is  in  particular  the  case  with  the 
five  very  short,  but  quite  parallel-fibred  muscles,  which  at  the 
inner  basal  surface  of  the  lantern  connect  the  five,  long,  movable 
chalk  ribs,  that  run  out  radially  from  the  central  oesophageal 
cavity  towards  the  periphery,  where  they  curve  down  over  the 
lateral  surfaces  of  the  lantern.  Besides  these  five  muscles, 
which  form  a  closed  ring,  and  are  each,  in  large  specimens,  I'O 
cm.  long,  and  about  4  mm.  broad,  the  other  larger  muscles, 
which  are  inserted  into  the  jaws,  and  move  the  teeth  set  into 
them,  and  also  fill  up  the  intermediate  space  between,  are  very 
convenient  for  experimental  purposes.  No  especial  preparation 
is  necessary  for  the  first  orientation  experiment.  It  is  sufficient 
to  divide  the  sea-urchin  with  scissors  into  an  upper  and  lower 
half,  breaking  away  as  much  of  the  shell  from  the  oval  part 
containing  the  lantern  as  will  give  convenient  admission  to  the 
electrodes.  After  drawing  the  teeth  with  forceps,  the  membranes 
that  partly  cover  and  partly  connect  the  muscles  nmst  also  be 
removed,  and  the  preparation  is  then  sufficiently  ready  for 
experiment.  If  it  is  now  dipped"  in  a  vessel  of  sea-water,  which 
is  as  indifferent  for  these  muscles  as  for  those  of  Holothuria,  so 
that  only  the  base  of  the  chalk  pyramid  with  the  ring  of  muscle 
projects  freely,  and  any  point  along  any  one  of  the  five  muscles 
is  brought  into  unipolar  contact  with  the  fine-pointed  kathode, 
while  the  other  unpolarisable  electrode  dips  into  the  water  of  the 
vessel,  the  formation  of  an  idio-muscular  swelling  will  be  even 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  239 

more  elegantly  demonstrated  than  in  the  longitudinal  muscles 
of  Holothuria.  With  appropriate  gradation  of  strength  of 
current  this  appearance  can  be  seen  at  every  possible  stage  of 
development.  The  transparent  nature  of  the  smooth  thin 
muscles,  as  well  as  their  promptness  of  reaction,  are  very  favour- 
able, and  it  would  be  difficult  to  find  any  other  object  in  which 
the  local  manifestations  of  excitation  at  the  kathode  can  be  so 
elegantly  demonstrated.  The  contracted  part  stands  out  with 
extraordinary  sharpness  and  plasticity  from  the  surrounding 
region  as  a  pale  opaque  bleb  with  a  peculiar  dull  lustre ;  it  rises 
quickly  upon  closure  of  the  current,  remains  unchanged  during 
its  passage,  and  only  sinks  down  again  gradually  when  the 
circuit  is  opened.  If  a  minimal  current  is  used  for  excitation, 
the  contraction  appears  more  and  more  localised  to  the  immediate 
proximity  of  the  point  of  exit,  gaining  in  amplitude  with  in- 
creasing intensity  of  current,  until  finally  the  kathodic  bleb  at 
the  electrode  spreads  over  the  whole  extension  of  the  muscle  in 
the  form  of  a  knotty  swelling,  and  as  the  muscle-substance  is,  as 
it  were,  drawn  up  on  either  side  to  form  this  swelling,  a  not 
inconsiderable  shortening  of  the  entire  muscle  follows.  But  it  is 
never  so  strongly  marked  as  with  unipolar  anodic  excitation. 

In  this  case,  when  the  current  is  closed,  a  marked  total  con- 
traction of  the  whole  muscle  makes  its  appearance,  so  that  the 
movable  points  of  insertion  are  brought  as  closely  together  as 
possible. 

The  muscle  appears  tensely  stretched, -and  at  first  seems  to 
be  uniformly  shortened  at  every  point.  This  last  effect  is  very 
striking  in  view  of  the  reactions  previously  described  for 
kathodic  excitation.  There  is  in  consequence  not  merely  no 
strong  local  contraction  at  the  anode,  but  on  applying  somewhat 
stronger  currents  there  is  an  actual  interruption  of  continuity  in 
the  nmscle.  If  the  electrode  (anode)  is  brought  into  contact 
with  any  point  of  the  free,  sharp  edge  of  a  muscle,  the  latter 
extends  itself  considerably  at  closure,  and  before  long  a  thin 
transparent  point  will  appear  at  the  electrode  (under  the  magni- 
fying lens),  upon  which  the  fibres  next  in  contact  to  it  break 
away,  and  curl  back  on  either  side.  If  the  electrode  is  advanced 
the  whole  muscle  will  sometimes  break  up  transversely,  the 
fibres  breaking  away  from  the  part  in  contact,  in  proportion  as 
the  layers  are  disturbed  deeper  and  deeper. 


240  ELECTRO-PHYSIOLOGY  chap. 

The  key  to  this  somewhat  startling  fact  seems  to  lie  in  the 
reaction  of  the  Holothurian  muscles,  as  described  above.  We  can 
hardly  doubt  that  in  both  cases  there  is  complete  conformity  in 
regard  to  kathodic  effects  of  excitation.  But  even  the  seemingly 
divergent  effects  in  unipolar  anodic  excitation  of  Echinus  muscles, 
must  really  be  traced  back  to  changes  analogous  with  those 
so  clearly  expressed  in  the  longitudinal  muscles  of  the  Holo- 
thurians.  Here  at  the  very  entrance  of  the  current  we  found  a 
local  relaxation,  marked  by  the  formation  of  an  attenuated  part 
from  which  a  contraction  that  is  well  marked  in  fresh  speci- 
mens develops  on  either  side,  and  produces  a  considerable  total 
shortening  of  the  muscle.  Now  if  a  short,  fine  muscle  of  identical 
or  similar  properties  were  stretched  betw^een  two  points  of  in- 
sertion, which  in  contracting  can  only  be  approximated  within 
certain  limits,  the  effect  of  the  kathodic  closure  excitation  would 
obviously  be  the  same  as  in  the  yielding  attachment  of  a  Holo- 
thurian muscle. 

With  unipolar  anodic  excitation  the  effect  is,  however,  quite 
different.  If  the  current  enters  at  any  point  along  the  muscle, 
and  local  relaxation  appears  after  closure,  or  if  the  part  in  con- 
tact remains  unexcited  while  a  marked  contraction  occurs  on 
either  side  of  it,  there  must  obviously,  if  the  point  of  insertion 
cannot  be  further  approximated,  be  an  interruption  of  continuity 
at  the  point  of  least  resistance. 

The  tearing  apart  at  the  anode  would  on  this  assumption  be 
referred  to  the  fact  that  in  unipolar  anodic  excitation  of  the 
muscle,  relaxation  occurs  at  the  contact  itself,  but  there  is  a 
marked  condition  of  tension  on  either  side  if  the  muscle,  on 
account  of  the  given  mechanical  conditions,  is  unable  to  contract 
further.  This  is  also  the  reason  why  Echinus  muscle  stimulated 
in  situ  does  not,  like  Holothuria,  exhibit  a  deep  canal  with  walls 
rising  round  it  at  the  anode,  but  only  a  tension  which  is  appar- 
ently uniform  at  every  point. 

The  two  last  cases  also  interpret  those  more  complicated 
instances,  where,  e.g.,  in  the  muscular  integument  of  many  worms, 
and  also  in  the  intestine  of  vertebrates,  two  systems  of  smooth 
muscle-cells  lie  superficially  directly  over  each  other,  so  that  the 
direction  of  fibres  in  both  is  at  right  angles  (30).  If  a  large 
earthworm,  paralysed  with  dilute  alcohol  (5  to  7  per  cent),  is  placed 
on  a  leading-off  stage,  which  is  constructed  of  several  layers  of 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  241 

filter-paper  or  salt  clay,  and  is  in  contact  with  one  (the  indifferent) 
electrode,  while  the  other  (a  fine  brush  electrode)  is  placed  on  the 
centre  of  the  dorsal  surface  of  one  of  the  broad  segments  at  the 
anterior  end  of  the  worm,  a  sufficiently  strong  current — given 
maximal  paralysis  of  voluntary  movements  and  reflexes — will 
throw  tlie  segment  in  direct  contact  (and  that  segment  only)  into 
circular  constriction,  in  which  state  it  will  persist  as  long  as  the 
current  remains  closed.  If  the  current  is  strong  and  the  ex- 
citability of  the  muscle  high,  this  constriction  (produced  by 
contraction  of  the  circular  muscles)  may  almost  obliterate  the 
lumen  of  the  body-cavity,  thus  of  course  producing  more  or  less 
passive  distortion  of  the  surrounding  parts,  and  of  the  immediately 
contiguous  segments  in  particular.  The  excitation  effect,  however, 
remains  localised  in  the  segment  in  direct  contact,  and  there  is  no 
propagation  of  contraction  in  the  form  of  a  peristaltic  wave. 
But  along  with  this  passive  contraction  of  the  adjacent  portions  of 
the  muscular  integument,  there  is  rarely  wanting  an  active 
decrease  in  height  of  the  contiguous  segments,  due  to  the  contrac- 
tion of  the  longitudinal  muscles,  which  is  most  strongly  marked 
in  the  immediate  proximity  of  the  constriction,  and  gradually 
diminishes  outwards,  so  that  it  is  never  perceptible  at  the 
whole  periphery  of  the  segments  affected,  but  only  at  the  side 
corresponding  with  the  seat  of  excitation.  Hence  we  must  be 
dealing  with  a  unilateral  contraction — mainly  active,  but  in  part 
passive  also — of  the  body-rings  adjacent  to  the  anodically  excited 
segment.  The  proof  that  this  is  a  genuine  shortening  of  the 
longitudinal  muscles  (apart  from  the  spatial  extension  of  the 
changes  produced  at  either  side  of  the  circular  muscle  contrac- 
tion, which  may  be  very  considerable)  lies  unquestionably  in 
the  important  decrease  in  height  of  the  segments  affected,  and 
the  only  doubtful  point  is  how  the  directly  excited  segment 
itself  reacts  under  these  conditions.  It  is  ijrima  facie  evident 
that  there  is  an  often  maximal  excitation  of  the  circular 
muscles,  while  perceptible  shortening  of  the  longitudinal  muscle 
on  the  other  hand  is  everywhere  absent.  This  cannot  perhaps 
be  determined  only  from  the  fact  that  there  is  no  apparent 
decrease  in  the  height  of  the  muscle-segment  concerned,  since 
the  two  layers  of  muscle  work  antagonistically  both  in  regard  to 
changes  in  length  (height),  and  in  breadth,  of  the  segment,  but 
on  the  other  hand  it  is  indisputable  that  cases  may  be  observed 

R 


242  ELECTRO-PHYSIOLOGY 


in  which  the  contraction  of  the  circular  muscles  is  com- 
paratively less  developed  than  the  contraction  of  the  longitudinal 
muscles,  on  either  side  of  the  ring  in  contact  with  the  anode, 
so  that  the  latter  is  only  constricted  in  an  inferior  degree ; 
nor  does  the  height  of  this  segment  diminish,  although  this  is 
in  a  marked  degree  characteristic  of  the  neighbouring  segments. 
Moreover,  there  is  another  feature  in  every  case,  which  seems 
to  be  of  importance  in  the  conception  of  the  anodic  effects  of 
excitation. 

If  the  contraction  of  the  circular  muscles  is  pronounced,  the 
excitation  appears  to  be  developed  with  approximate  uniformity 
at   every   point   of  the  muscle -ring,  as    though   the   process    of 
excitation,  i.e.   contraction,  starting   from    the  anode,  was  trans- 
planted  on   either   side  from  section   to  section.      This   idea   at 
once  suggested  itself  from  an  unprejudiced  consideration  of  the 
effects  of  excitation.      But  if  the  ring-shaped  constriction  is  not 
maximal,  so  that  the  part  of  the  segment  in  contact  with   the 
anode  remains  visible,  it  can   usually  be  seen   (at  least  under 
the  magnifying  lens)  at  the  actual  point  where  the  current  enters, 
as    well    as    in    the    immediate    proximity,    not    only   that    the 
contraction  of  the  longitudinal  muscle  is  wanting,  but  that  there 
is  not   even   any  perceptible   contraction  of  the  circular  muscles. 
This  is  especially  plain  when  the  surface  of  the  worm  has  dried 
from  evaporation,  and  consequently  become  less  elastic.      It  then 
appears  very  elegantly  that  fine  cross -wrinkles  arise   from  the 
involution   of  the   epidermis    on   the   surface   of  the    contracted 
ring ;  these  are  plainly  visible  at  either  side  of  the  electrode,  but 
fail  altogether  in  the  immediate  proximity  of  the  anodic  contact. 
The  electrode  must  be  only  just  moist  in  this  experiment,  so  as  to 
avoid  wetting  the  seat  of  excitation.     In  every  such  case  a  directly 
relaxing  (inhibitory)  effect  of  the  anode   may  be  demonstrated, 
if  the  contact  is  pushed,  during  closure  of  the  current,  towards 
any  point  of  the  excited  segment  in  which  the  contraction  has 
already  produced  obvious  transverse  wrinkles.      As  soon  as  such 
a  spot  is  brought  into  contact  with  the  anode  it  begins  to  smooth 
itself,  and  gives  the  impression  that — notwithstanding  the  con- 
traction  of  adjacent   parts  of  the   muscle-ring — relaxation   and 
lengthening  occur  at  the  actual  seat  of  contact.     It  is  by  no  means 
rare  in  longitudinal  as  in  circular  muscles,  to  find  this  failure 
of  contraction  at   the  anode  itself,  still  more  plainly  marked  by 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  243 

the  formation  of  a  little  superficial  dint  or  hollow,  the  origin  of 
which  can  be  easily  explained.  It  is  obvious  that  when  no 
excitation  occurs  at  the  point  at  which  two  muscle  bundles  of 
equal  breadth  cross  at  right  angles,  while,  on  the  other  hand,  the 
arms  of  the  cross  beyond  the  juncture  do  contract — the  more 
strongly  in  proportion  as  the  section  is  applied  nearer  the 
crossing  point — a  quadratic  hollow,  bordered  by  four  large  swell- 
ings of  equal  dimensions,  must  be  developed.  An  exact  dia- 
grammatic representation  of  this  effect  in  the  excited  segment  of 
the  worm  is  from  anatomical  reasons  obviously  impossible,  but  it  can 
often  be  seen  that  the  segment  in  contact  with  the  anode  is  drawn 
in  at  that  point,  and  appears  to  be  surrounded  by  bulging  walls, 
which  must  be  referred  partly  to  the  portions  of  the  circular 
muscles  contracting  upon  themselves  in  the  segment,  partly  to  the 
equally  shortened  longitudinal  muscles  of  the  next  adjacent 
segment. 

The  whole  effect  can  often  be  brought  out  more  strongly  if, 
with  the  current  closed,  two  contiguous  segments  are  repeatedly 
stroked  at  right  angles  to  the  direction  of  the  fibres  with  the 
brush  electrode,  upon  which  both  the  unexcited  surface  and  the 
area  of  contraction  become  larger,  and  stand  out  more  sharply 
from  one  another. 

Most  convincing  of  all,  however,  is  the  local  inhibitory  effect 
of  the  anode  (siipra)  at  those  points,  where  either  the  longitudinal 
or  circular  muscles,  or  both,  seem  for  some  reason  to  be  per- 
manently contracted.  The  local  relaxation  of  both  systems  of 
fibres  at  the  segment  in  direct  contact  is  then  very  plain,  and 
quite  unmistakable. 

The  changes  at  the  kathode  are  no  less  striking  than  at  the 
anode,  when  the  muscular  sheath  of  Lumbricus  is  excited  electric- 
ally during  closure.  It  would  almost  be  sufficient  to  say  that 
they  express  themselves  by  a  direct  antagonism,  but  it  is  advisable 
to  describe  them  a  little  more  in  detail. 

If  attention  is  directed  solely  to  the  segment  in  contact  with 
the  electrode,  the  antithesis  of  the  anodic  and  kathodic  excitation 
effects  is  very  striking,  and  would  (without  minute  examina- 
tion) suggest  that  with  closure  of  current  at  the  anode  the 
circular  muscles,  at  the  kathode  the  longitudinal  muscles,  are 
exclusively  excited. 

It  has  already  been  shown,  however,  that  the  relations  are  by 


244  ELECTRO-PHYSIOLOGY 


no  means  so  simple  at  the  anode,  nor  are  they  more  so  with 
kathodic  excitation.  There  can  be  no  doubt  that  the  longi- 
tudinal muscles  of  the  directly  stimulated  section  are  excited,  but 
we  may  question,  for  reasons  to  be  stated  below,  whether  the 
ring-muscles  are  not  also,  at  least  locally,  excited  at  the  point 
of  contact. 

The  first  desideratum,  in  an  exact  observation,  is  not  to 
employ  too  strong  a  current,  since  the  problem  will  otherwise  be 
unduly  complicated.  It  must  be  remarked  once  more  that  the 
results  of  bipolar,  coincide  exactly  with  those  of  unipolar, 
excitation.  The  more  striking  change  is,  as  we  have  seen,  the 
shortening  (decrease  in  height)  of  the  body -rings  implicated. 
This  is  not,  as  a  rule,  uniform  throughout  the  periphery,  but  is 
essentially  confined  to  the  immediate  proximity  of  the  kathode. 
Here,  in  consequence  of  the  longitudinal  muscular  contraction,  the 
segment  involved  appears  in  relief  as  a  swollen  blister,  between 
the  contiguous  segments.  The  latter  participate  equally  in  the 
stimulation  with  stronger  currents,  so  that  on  closure  of  the 
current  the  longitudinal  muscular  contraction,  extending  over 
several  segments,  causes  a  more  or  less  pronounced  swelling  to 
spring  up,  which  is  mainly  confined  to  the  point  directly 
excited,  rises  most  abruptly  under  the  kathode  itself,  and  falls 
away  tolerably  quickly  on  either  side  of  it.  If  the  tract  of 
kathodic  excitation  is  examined  at  an  appropriate  strength  of 
current,  with  a  magnifying  lens,  particular  attention  being  given 
to  the  appearance  of  excitation  effects  in  the  segment  directly  in 
contact  with  the  electrode  at  the  moment  of  closure,  it  is  not 
usually  difficult  to  ascertain  positively  that  there  is  also 
at  that  point  a  contraction  of  the  circular  muscles,  localised 
to  the  kathode,  which  only  remains  unnoticed  with  less  atten- 
tive observation,  because  its  spatial  restriction  prevents  any 
perceptible  diminution  of  diameter  in  the  muscle -ring.  This 
effect  is  limited,  with  the  application  of  moderate  currents,  to  the 
segment  directly  excited,  and  in  consequence  a  marked,  lumpy 
protuberance  is  often  visible  at  the  point  of  contact,  which 
is  no  doubt  due  to  the  disguised  and  local  contraction  of  the 
longitudinal  and  circular  muscles.  In  order  to  attest  the  latter 
it  is  important  to  note  that  in  the  muscular  integument  the  layer 
of  circular  muscles  (conversely  to  the  vertebrate  intestine)  lies 
externally,  and  is  thus  directly  accessible  to  observation.      Other- 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  245 

wise  it  would  be  difficult  to  come  to  any  conclusions  as  to  the 
changes  in  the  circular  muscles,  particularly  with  kathodic 
excitation  (Fiirst,  30). 

We  have  so  far  been  investigating  the  manifestations  of 
excitation  at  closure  only.  It  remains  to  add  a  few  words  as  to 
the  polar  effects  that  appear  on  opening  the  circuit.  As  in  most 
other  cases,  so  here,  it  is  found  that  stronger  currents  and  pro- 
longed duration  of  closure  are  essential  to  produce  effective  break 
excitation.  It  need  hardly  be  added  that  individual  differences 
of  excitability  in  the  preparation  are  also  prominent  factors.  The 
opening  excitation  effects,  at  least  in  Lumbricus,  are  never  so 
sharply  defined  as  those  at  closure.  The  most  definite  appearance 
is  a  contraction  of  the  circular  muscles — similar  to  that  of  the 
anodic  closure — at  the  previously  kathodic  segment,  on  opening  the 
circuit ;  yet  it  is  difficult  to  decide  with  certainty  whether  the 
contraction  spreads  itself  in  this  case,  as  in  anodic  make  excitation, 
on  either  side  of  a  relaxed  point.  Yet  more  difficult  is  it  to 
determine  the  nature  of  the  co-operation  of  the  longitudinal 
muscles,  as  appearing  under  certain  conditions  after  strong  anodic 
excitation  of  a  segment  on  breaking  the  current.  It  is  partly  due 
to  the  comparatively  slow  equalisation  of  the  excitation  effects 
after  closure,  which — at  least  sometimes — produces  a  superposition 
of  what  may  be  taken  as  the  antagonistic  effects  of  closing  and 
opening  the  current,  by  which  the  question  is  further  complicated. 

The  effects  of  electrical  excitation  in  the  leech,  and  in 
Arenicola  (29)  in  particular,  are  quite  as  characteristic  as  in  the 
muscular  integument  of  the  earthworm.  Here,  too,  the  most 
prominent  effects  at  closure  of  the  current  are,  on  the  one  hand 
(at  the  anode),  contraction  of  the  circular  muscles  of  the  segment 
directly  in  contact  with  the  electrode ;  on  the  other  hand  (at  the 
kathode),  the  marked  shortening  of  the  same  in  consequence  of 
the  contraction  of  the  longitudinal  muscles.  Owing  to  the  small 
distance  between  the  transverse  furrows  which  encircle  the  worm's 
body,  the  kathodic  effects  of  excitation  spread,  more  particularly 
in  the  leech,  over  a  large  number  of  segments,  whilst  in  a  long 
body-ring,  e.g.  at  the  anterior  end  of  Lumbricus,  the  kathodic 
contraction  of  the  longitudinal  muscles  (at  least  with  weak  excita- 
tion) is  often  only  segmentally  developed.  The  flat  shape  of  the 
body  in  the  leech,  moreover,  brings  out  plainly  the  localisation 
of  effects  of  kathodic  excitation  to  the  dorsal  surface  excited. 


246  ELECTRO-PHYSIOLOGY  chap. 

There  is  never  an  undulatory  transmission  of  the  contraction  over 
large  sections  of  the  worm-body.  On  the  contrary,  these  remain 
fixed  in  the  expansion  determined  at  closure  as  long  as  the 
current  is  passing,  and  this  applies  as  well  to  the  anodic  circular, 
as  to  the  kathodic  longitudinal,  muscular  contraction.  In  the 
leech  also  it  is  certain  that  the  latter  does  not  appear  singly,  but 
is  accompanied  by  a  simultaneous  localised  contraction  of  the 
circular  muscles  at  the  point  of  contact  with  the  electrode. 
A  small  but  plainly  visible  swelling  accordingly  starts  up  under 
the  electrode,  running  transversely  to  the  fibres  of  the  circular 
muscles,  and,  as  it  were,  opposed  to  the  expansion  produced  by 
the  contraction  of  the  longitudinal  muscles.  No  trace  of  excitation 
is  visible  in  the  same  bundle  of  circular  fibres  beyond  the  small, 
sharply-defined  swelling.  Where  a  perceptible  ("  tonic  ")  contrac- 
tion existed  already  before  closure,  it  may  be  seen  to  expand  into 
the  localised  swelling  at  the  point  of  current  exit.  At  both  sides  of 
this  there  will  then  be  a  visible  relaxation  of  the  circular  muscles, 
so  that  at  times  the  lateral  parts  of  the  segment  bulge  out 
bladderwise,  convexly  to  the  exterior,  thus  producing  a  very 
characteristic,  and  more  or  less  complicated,  change  of  form  in  the 
muscular  integument  at  the  proximity  of  the  electrode.  The 
swelling  caused  by  the  local  contraction  of  the  longitudinal 
muscles  is  also  sharply  defined  on  either  side,  although,  as  stated, 
it  extends  over  several  segments.  At  break  of  the  circuit  the 
changes  described  (Fiirst,  I.e.)  are  either  equalised  simply,  or 
(with  stronger  currents,  and  longer  duration  of  closure)  a  break 
excitation  makes  its  appearance,  as  in  the  earthworm,  by  a 
shortening  of  the  circular  muscles,  which  extends  over  large  areas 
of  the  previously  excited  segment,  producing  a  more  or  less  pro- 
nounced segmental  constriction — a  change,  of  which  the  resem- 
blance to  the  effects  of  anodic  make  excitation  is  lorima  facie 
evident,  although  it  is  difficult  to  demonstrate  complete  coinci- 
dence in  the  two  cases.  While  on  bringing  any  points  of  the 
upper  surface  of  the  muscular  investment  of  Hirudo  into 
contact  with  the  kathode,  there  is,  in  consequence  of  the  simul- 
taneous shortening  of  the  longitudinal  and  circular  muscles,  a 
general  pressure  of  the  muscle-substance  from  all  sides  towards 
the  point  where  the  current  leaves  the  muscle,  a  precisely  opposite 
effect  appears  with  anodic  excitation.  It  is  even  more  evident 
in  Hirudo  than  in  Lumbricus,  that  the  segment  in  contact  with 


in  ELECTRICAL  EXCITATIOX  OF  MUSCLE  247 

the  anode  remains  unexcited  at  the  point  of  contact  at  the 
instant  of  closure,  or  relaxed  if  there  has  been  a  previous  tonus. 
In  this  example  a  good  indication  of  contraction,  or  relaxation,  of 
the  circular  muscles  is  afforded  by  the  relative  distance  of  the 
line  transverse  lines  of  the  skin,  through  which  each  segment 
vertical  to  the  direction  of  fibres  in  the  circular  muscles  exhibits 
parallel  strise.  At  every  shortening  of  the  circular  muscles, 
these  striae  approximate  at  the  contracted  parts ;  at  every  exten- 
sion the  space  between  them  gets  larger.  This  last  occurs 
unmistakably  at  closure  of  the  current  in  the  immediate  proximity 
of  the  anodic  contact,  together  with  a  marked  contraction,  and 
subsequent  circular  constriction,  of  the  segments  implicated. 
This  also  applies,  at  the  same  point,  to  the  longitudinal  muscles, 
which  do  not  shorten  at  the  electrode  itself;  the  height  of  the 
segment  does  not  alter.  On  the  other  hand,  as  in  the  earthworm, 
a  more  or  less  extensive  contraction  of  the  longitudinal  muscles 
appears  in  the  segments  implicated  on  either  side  of  the  circular 
constriction,  in  proportion  with  the  strength  of  the  current ;  this 
is  most  developed  in  the  immediate  vicinity  of  the  body-ring  in 
contact  with  the  anode,  and  gradually  decreases  outwards. 

All  these  facts  combine  to  show  that  the  so-called  smooth 
muscles  of  very  different  invertebrate  animals  exhibit,  as  regards 
their  reaction  to  the  electrical  current,  a  wide,  almost  complete, 
uniformity  of  behaviour.  Here,  too,  the  law  of  polar  excitation 
prevails  in  general,  although  certain  effects  appear  which  are 
apparently  without  analogy  in  striated  muscle.  As  a  general 
rule,  the  proposition  still  holds  that  at  closure  of  a  sufficiently 
strong  current,  excitation  and  contraction  follow  at  the  physio- 
logical kathode.  Where  at  first  sight  there  seem  to  be  exceptions 
{e.g.  in  the  circular  fibres  of  the  muscular  integument  of  worms), 
more  exact  observation  brings  them  under  the  same  law. 
Especially  notable  is  the  fact  that  the  kathodic  closure  excitation  is 
localised  in  every  instance  to  the  point  of  exit  of  the  current,  and  its 
immediate  proximity,  in  the  form  of  a  loccd  " idio- muscular" 
swelling  {persistent  closure  contraction).  In  no  case  is  an  undulatory 
propagation  of  the  contraction  to  be  detected. 

Further,  in  conformity  with  the  law  of  polar  excitation, 
there  is  at  closure  of  the  current  no  loccdised  excitcdion  cd  the  anode, 
hut  rather  an  inhibition  of  a  previously  existing  condition  of  ex- 
citation, ivhile  an  op)ening  excitation,  on   the  contrary,  does  occur 


248  ELECTRO-PHYSIOLOGY  chap. 

at  this  point,  under  some  conditions.  That,  notwithstanding,  a 
frequently  well-marked  total  contraction  of  the  muscle  bundle 
should  almost  invariably  occur  with  unipolar  anodic  excitation, 
is  because  the  fundamental  excitation  at  closure  of  the  current 
does  not  proceed  from  the  anode  itself,  but  originates  in  the 
region  proximal  to  it,  as  will  presently  be  described.  This 
accounts  for  the  somewhat  surprising  fact  that  closure  of  current 
at  the  anode,  in  electrical  excitation  of  the  worm's  integument, 
produces  a  (sometimes  maximal)  constriction  of  the  segment  in 
direct  contact,  and  also  accounts  for  the  marked  shortening  of 
Echinus  and  Holothurian  muscles  in  unipolar  anodic  excitation,  as 
well  as  the  no  less  striking  rupture  of  the  former  at  the  spot 
at  which  current  enters. 

From  this  point  of  view  it  is  easy  to  explain  the  excitation 
effects  in  the  intestine  of  invertebrates  (31)  —  at  first  sight 
so  unexpected  and  irregvilar.  If  a  given  surface -point  of  a 
quiescent  loop  of  the  small  intestine  of  any  mammal  is  brought 
into  contact  with  the  anodic  electrode,  at  sufficient  intensity  of 
current,  while  the  kathode  is  again  applied  to  any  indifferent  part 
of  the  body  (liver,  stomach,  etc.),  a  circular  constriction  is  formed, 
as  in  worms,  and  may,  under  some  conditions,  lead  to  the 
complete  closing  up  of  the  intestinal  tube  at  the  point  in  question. 
This  contraction  persists  throughout  the  duration  of  closure,  pro- 
vided the  latter  does  not  extend  over  too  long  a  period,  and 
equalises  itself  again  without  much  delay  when  the  current  is 
broken.  This  effect  of  excitation  can  be  very  well  seen  in  loops 
of  the  intestine  that  are  moderately  extended  by  fluids  or  gases. 
Provided  the  exposed  intestine  is  not  unduly  cooled,  and  is  still 
highly  excitable,  there  will  at  closure  of  the  current,  in  addition 
to  the  local  contraction  of  the  circular  muscles  at  the  anode,  be  a 
more  or  less  evident  peristaltic,  or  anti-peristaltic,  movement  in 
the  proximity  of  the  point  directly  excited,  of  which  in  this  case 
it  is  hardly  possible  to  say  whether  it  is  directly  caused  by  a 
branch  of  the  current,  or  is  carried  on  from  the  primary  seat  of 
excitation.  We  shall  see  later  that  under  certain  conditions  the 
anode  does  actually  become  the  point  of  departure  of  peristaltic 
contractions  spreading  on  either  side,  while  in  other  cases  a 
merely  local  constriction  appears.  Various  sections  of  the 
intestine  in  this  respect  give  a  uniform  reaction,  and  at  most 
show  differences  in  degree,  which  are  due  to  the  unequal  develop- 


in  ELECTRICAL  EXCITATION  OF  MUSCLE  249 

ment  of  the  circular  muscle  layer.  Thus  in  the  thin -walled 
and  usually  replete  colon  of  Herbivora,  the  constriction  does  not 
usually  include  the  entire  periphery,  but  only  forms  a  few,  or 
several,  deep  segmental  furrows. 

The  effect  is  very  different  on  reversing  the  current  with 
kathodic  excitation  of  the  intestine.  We  cannot  entirely  follow 
Schillbach,  who  first  investigated  the  effects  of  electrical  excitation 
of  the  intestine,  when  he  speaks  in  this  case  briefly  of  a  local 
contraction,  and  only  sees  as  an  essential  difference  in  the  work- 
ing of  the  two  electrodes  that  there  is  an  appearance  "  at  the 
anode  of  peristaltic  waves,  particularly  in  an  upward  direction," 
while  at  the  kathode,  on  the  contrary,  the  contractions  are 
wholly  local.  For,  on  the  one  hand,  the  appearance  of  a  contrac- 
tion limited  to  the  seat  of  direct  excitation  is  very  general  at  the 
anode  also ;  while,  on  the  other,  it  must  be  admitted  that  the 
visible  effects  of  excitation  at  the  seat  of  the  kathode  always 
exhibit  a  fundamentally  distinct  character  from  the  effects  of 
excitation  at  the  anode.  While  the  typical  circular  constriction 
is  never  wanting  at  the  anode,  and  appears  similarly  at  the  small 
intestine,  as  well  as  at  the  colon,  or  rectum,  the  manifestations  of 
excitation  at  the  kathode  develop  very  variously  both  in  different 
species  of  animals  and  in  different  intestinal  sections  of  the  same 
animal.  In  rabbits,  guinea-pigs,  and  mice,  complete  constriction 
of  the  tube  of  the  intestine  occurs  at  the  anode,  on  closure  of  the 
current,  while  at  the  kathodic  contact  the  change  is  scarcely 
perceptible,  and  it  is  only  by  very  exact  observation  that  the 
formation  of  a  small,  fluted  thickening  can  be  detected,  and, 
corresponding  with  it,  in  its  immediate  proximity,  a  flat,  dinted 
constriction  of  the  upper  surface.  This  longitudinal  fluting, 
which  is  only  indicated  at  the  point  where  the  current  leaves  the 
intestine  of  rabbits  or  guinea-pigs,  appears  invariably  in  that  of 
cats  or  dogs  as  a  crest-like,  prominent  expansion,  parallel  with  the 
long  axis  of  the  intestinal  canal,  and,  like  a  scar,  producing  con- 
striction of  the  tract  lying  immediately  around  it,  so  that  on  that 
side  of  the  intestinal  wall  a  flat,  dinted  depression  is  formed,  with 
the  fluting  already  referred  to  springing  from  its  centre.  These 
changes  also  persist  during  the  closure  of  the  current,  and  only 
equalise  themselves  more  or  less  rapidly  when  the  circuit  is  broken. 
The  manifestations  of  polar  excitation  in  the  different  sections  of 
the    colon  of  Herbivores   are   also   interesting — the    anatomical 


250  ELECTRO-PHYSIOLOGY 


arrangement  of  the  muscular  layers  presenting  unmistakable 
analogies  with  the  relations  described  in  Holothuria.  In  neither 
case  do  the  external  longitudinal  muscles  of  the  intestine  present 
a  coherent  layer ;  they  are  either  exclusively  (holothurian),  or  pre- 
dominantly (large  intestine),  compressed  into  single  band-like  striae 
(t&eni?e),  between  which  the  circular  muscles  are  visible.  If  an 
electrical  current  leaves  the  muscle  at  any  point  of  such  a  tcenia, 
an  obvious,  localised,  persistent  contraction  appears,  which  is 
absent  when  the  current  enters  at  the  same  spot ;  then,  on 
the  contrary,  there  is  usually  segmental  constriction  of  the  wall 
of  the  intestine,  due  to  excitation  of  the  circular  muscles.  If  the 
anode  happens  to  fall  on  any  part  of  the  surface  of  a  saccule, 
the  last-named  consequences  of  excitation  occur  only  the  more 
plainly.  If,  on  the  contrary,  the  current  leaves  by  the  surface  of 
a  saccule,  a  small,  scar-like  swelling  will  appear  (running  at 
right  angles  with  the  direction  of  the  fibres),  which  remains 
localised  to  the  immediate  proximity  of  the  kathode,  and — as 
may  be  recognised  with  artificial  enlargement — is  essentially 
caused  by  a  local  persistent  contraction  of  the  circular  muscle- 
fibres  only.  This  appearance  is  throughout  analogous  with  the 
small,  sharply-defined  transverse  swelling  of  Holothurian  circular 
muscles  apparent  on  kathodic  excitation.  This  local  kathodic 
excitation  of  the  circular  muscles  of  the  intestine  is  less  visible, 
for  obvious  reasons,  in  all  cases  where  a  longitudinal  muscular 
layer  of  considerable  thickness  is  present.  Yet  the  peculiar 
dinted  constriction  of  the  upper  surface  of  the  small  intestine, 
from  the  centre  of  which  the  scar-like  swelling  arises,  must  be 
referred  partly  to  the  local  kathodic  excitation  of  the  circular 
muscles  covered  by  the  longitudinal  fibres.  So  too,  the  tendinous 
origin  of  a  taenia  of  the  large  intestine  appears  with  kathodic 
excitation  to  be  concerned  in  the  production  of  a  local  circular 
muscle  swelling.  If  the  peculiar  and  characteristic  reaction 
of  the  circular  muscles  of  Holothuria  on  anodic  excitation,  as  well 
as  the  corresponding  excitation  effects  in  the  muscular  integu- 
ment of  worms,  is  remembered,  there  can  hardly  be  a  doubt  that 
the  circular,  or  segmental,  constriction  of  the  intestinal  wall  at  the 
anode  is  due  to  the  same  causes.  The  relations  are  not  indeed 
as  clear  and  easily  recognised  as  in  the  former  case,  and  least  so 
in  the  small  intestine.  The  well-filled  colon  of  Herbivores  seems 
much  more  appropriate  to  these  manifestations.      Here,  with  weak 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  251 

currents,  the  contraction  at  the  anode  is  not  total,  and  under 
certain  conditions,  particularly  when  the  surface  of  the  intestine 
has  become  dry,  it  is  evident  that  the  immediate  proximity  of 
the  anode  remains  smooth  at  closure  of  the  circuit,  while  in 
consequence  of  the  contraction  of  the  circular  muscles,  innumer- 
able wrinkles  are  formed  on  both  sides  of  it.  Nor  are  the 
longitudinal  muscle  bundles  of  the  ttenias  unexcited  if  the  anode 
is  placed  anywhere  along  their  course,  only  the  effects  are  more 
easily  overlooked  in  this  case.  The  immediate  proximity  of  the 
anode  is  again  unexcited,  while  contraction  occurs  in  the  neighbour- 
ing region.  In  the  thin  intestine,  where  the  anatomical  relations 
are  still  more  unfavourable  to  electrical  excitation  than  in  the 
muscular  integument  of  worms,  the  corresponding  manifestations 
of  excitation,  as  described,  are  very  difficult  to  analyse  in  detail, 
and  only  the  marked  and  extended  closure  contraction  of  the 
circular  muscles  remains  as  a  visible  effect  at  the  anode,  along 
with  the  local  shortening  of  the  longitudinal  fibres  at  the  kathode. 
It  cannot,  however,  be  doubted  that  in  the  first  case  the  longi- 
tudinal muscles,  in  the  second  (at  least  with  strong  currents)  the 
circular  muscles,  also,  are  excited  simultaneously,  and  to  the  same 
degree  (29). 

With  the  last-described  experiments  on  the  intestine  of  warm- 
blooded animals,  must  naturally  be  classed  the  results  of  Engel- 
mann's  extensive  experimental  investigation  on  the  electrical  ex- 
citation of  the  ureter  (5).  It  is  obvious,  in  view  of  the  inferior 
size  of  this  tube,  which  consists  of  circular  and  longitudinal 
muscles  arranged  similarly  to  the  intestine,  that  the  finer  details 
of  changes  of  form  in  the  two  muscular  layers  at  the  poles  of  the 
exciting  current  are  here  much  harder  to  recognise  than  in  the 
previous  cases.  For  this  reason,  an  efi'ect  which  only  appears 
exceptionally  in  the  intestine,  comes  prominently  forward  in  the 
ureter,  i.e.  the  peristaltic  progress  of  excitation,  or  contraction, 
from  its  starting-point.  Schillbach  (32)  states,  that  on  excit- 
ing the  intestine  with  the  constant  current,  "  a  contraction 
localised  to  the  seat  of  excitation  formed  itself  at  the  kathode," 
while  at  the  anode  a  local  contraction  appeared,  which  in  a  few 
seconds  was  transformed  into  a  marked  peristaltic  contraction 
upwards  and  downwards.  We  have  frequently,  in  excised  and 
still  living  (warmed)  pieces  of  intestine,  observed  the  peristaltic 
or    anti- peristaltic   progress   of   the   contraction   of  the    circular 


252  ELECTRO-PHYSIOLOGY 


muscles  discharged  at  the  anode.  But  just  as  the  propagation 
of  a  localised  excitation  in  the  muscle  of  the  intestine  depends 
upon  different,  and  so  far  not  exactly  determined,  data,  so  too 
with  polar  effects  of  excitation.  On  the  one  hand,  a  high 
excitability  of  the  excitable  parts  is  apparently  essential,  while 
on  the  other,  the  nervous  mechanism  of  the  intestine  itself  seems 
again  to  play  a  very  important  part  in  the  bringing  about 
of  progressive  contraction.  Most  authors  incline  to  the  view 
that  both  the  normal  and  the  artificially  excited  peristalsis  are 
caused  s6lely  and  invariably  by  the  intestinal  nervous  system 
(Nothnagel,  Luderitz,  33).  Without  taking  a  definite  position 
in  this  question,  which  was  discussed  above,  the  possibility  of 
propagating  the  excitation  effects  discharged  at  the  poles  of 
the  constant  current  may  be  suggested.  With  the  application  of 
strong  currents  Liideritz  observed  this  at  the  positive  as  well  as 
at  the  negative  pole  ;  but  the  kathode  seemed  to  produce  a 
stronger  effect  than  the  anode.  "  In  the  rabbit  and  guinea-pig 
this  effect  appeared  in  well-marked  cases  as  a  contraction  of  the 
longitudinal  muscle  of  the  intestine,  extending  for  several  cms., 
upwards  and  downwards,  from  the  electrode,  accompanied  by  a 
contraction  of  the  circular  muscles  running  exclusively,  or  chiefly, 
in  the  direction  of  the  pylorus ;  in  the  cat  the  contraction  of  the 
circular  muscles  may  run  upwards  and  downwards,  or  in  the 
direction  of  the  pylorus  "  (33,  p.  14). 

In  contrast  with  these  uncertain,  and  still  unexplained, 
data,  the  effects  of  electrical  excitation  of  the  ureter  are 
characterised  as  well  by  the  certainty  of  their  appearance 
as  by  their  great  regularity.  The  thorough  investigations 
of  Engelmann  showed  that — apart  from  the  slowness  of  the 
reactions — there  is  complete  conformity  with  regard  to  the 
polar  manifestations  of  excitation,  between  the  ureter  and 
striated  skeletal  muscle,  so  that  these  observations  give  cogent 
support  to  the  theory  of  the  unlimited  applicability  of  the  law  of 
polar  excitation.  It  is,  therefore,  at  first  sight  the  more  sur- 
prising that,  so  long  as  the  ureter  remains  in  situ,  the  effects  of 
electrical  excitation  with  the  constant  current  are  diametrically 
opposite  to  what  might  be  expected  from  Engelmann's  investiga- 
tions. On  applying  unpolarisable  electrodes  to  two  points  along 
the  rabbit's  ureter,  after  exposing  it  with  the  utmost  care  and  avoid- 
ance of  unnecessary  cooling,  Engelmann  found  with  closure  of  the 


ELECTRICAL  EXCITATION  OF  MUSCLE 


battery  current  that  the  muscular  tube  contracted  at  the  spot 
in  contact  with  the  kathode,  after  a  shorter  or  longer,  but  always 
directly  perceptible,  latent  period,  while  the  whole  intrapolar 
area,  as  well  as  the  anode,  remained  quiescent  at  the  same  time. 
Immediately  after,  a  wave  of  contraction  (similar  to  that  which 
follows  on  localised  mechanical  excitation)  starts  from  the 
kathode,  in  both  the  peristaltic  and  the  anti-peristaltic  direction. 
Just  as  the  make  excitation  starts  from  the  kathode,  Engelmann 
found  that  the  break  excitation  proceeds  exclusively  from  the 
anode :  the  contraction  always  begins  exactly  at  the  point  where 
current  had  previously  entered  the  ureter  through  the  electrode, 
never  at  the  same  moment  in  any  larger  area  of  the  tract 
traversed.  Here,  as  in  striated  muscle,  the  opening  of  the 
constant  current  is  usually  a  weaker  stimulus  than  its  closure,  so 
that  greater  intensity  of  current,  and  longer  closure  in  particular, 
is  required  to  produce  any  visible  consequences.  According  to 
Engelmann,  induced  currents  work  exactly  like  constant  currents 
of  very  short  duration  (current  impacts),  i.e.,  as  a  rule,  they 
only  act  as  make  stimuli,  in  which  excitation  proceeds  from  the 
kathode.  It  is  only  with  very  high  excitability,  and  currents  of 
great  strength,  that  the  contraction  appears  under  certain  condi- 
tions to  begin  at  both  poles  simultaneously. 

If  in  the  guinea-pig,  or  rabbit,  the  two  electrodes  are  applied, 
after  removing  the  viscera,  to  different  points  of  the  ureter  in 
situ,  or  if  one  electrode  only  is  brought  into  contact  with  any 
given  point,  the  other  being  applied  to  some  indifferent  part  of 
the  body,  the  excitation  at  closure  will  invariably  proceed  from 
the  anode.  Under  such  conditions  there  is  never  kathodic 
closure,  or  anodic  opening,  excitation. 

With  both  the  weakest  and  strongest  possible  currents, 
and,  as  a  rule,  independently  of  the  position  of  the  electrodes, 
and  the  direction  of  the  current,  the  ureter  is  always  con- 
stricted first  at  the  anode,  on  closing  the  circuit,  after  which  the 
wave  progresses  in  both  directions  as  described  by  Engelmann. 
The  same  applies  to  the  break  excitation,  which  after  prolonoed 
closure,  with  sufficiently  strong  currents,  appears  at  the  kathode. 
The  nature  of  the  contraction  leaves  no  doubt  that  there  is  in 
both  cases  simultaneous  excitation  of  the  circular  and  lonefitudinal 
muscles.  The  smallness  of  the  object  makes  it  ditiicult  to  decide 
with  certainty  whether  the  closure  contraction  really  proceeds 


254  ELECTRO-PHYSIOLOGY 


from  the  point  of  contact  of  the  anode  with  the  ureter,  and 
whether,  on  the  other  hand,  there  is  local  continuous  contraction 
at  the  kathode.  The  latter  may  indeed  be  ascertained  by  means 
of  the  magnifying  lens,  so  that  it  can  hardly  be  doubted  that 
the  polar  excitation  effects  in  the  ureter  in  situ  are  manifesta- 
tions analogous  with  the  corresponding  effects  of  excitation  in 
the  intestine. 

The  striking  opposition  between  Engelmann's  data,  and  the 
results  of  experiments  on  the  organ  in  situ,  suggests  that  the 
apparent  reversal  of  polar  effects  depends  essentially  upon  differ- 
ences in  the  physical  conditions,  and  in  particular  on  the  distribu- 
tion of  current.  Experiments  directed  to  this  end  have  confirmed 
the  correctness  of  the  assumption,  and  may  also  furnish  the  key 
to  the  explanation  of  the  manifestations  which  appear  in  many 
other  smooth  muscular  parts  in  the  proximity  of  the  anode,  and 
which  we  have  previously  referred  to.  Since  the  excised  ureter 
of  mammals  is  still  excitable  after  several  hours,  if  warmed  to 
body-temperature,  it  is  easy  to  experiment  on  it  under  different 
conditions.  If  such  a  preparation  is  laid  upon  a  glass  plate, 
warmed  from  below  at  38—40'',  and  wetted  with  physiologica 
salt  solution,  or  better,  with  a  small  strip  of  moist  filter-paper,  the 
consequences  of  excitation,  when  the  electrodes  are  applied  any- 
where along  the  muscle,  coincide  in  respect  of  localisation  with 
Engelmann's  results  from  the  ureter  of  the  living  animal.  It 
appears  as  clearly  as  can  be  desired,  however  the  electrodes  are 
applied,  that  the  ureter  lying  loosely  upon  its  attachment  con- 
stricts at  the  kathode  at  the  moment  of  closure,  after  which  the 
contraction  progresses  in  undulations,  or  in  one  or  the  other  direc- 
tion. The  same  occurs  at  the  anode  with  stronger  currents,  and 
longer  duration  of  closure,  on  opening  the  circuit.  If  the  excised 
ureter  is  then,  without  otherwise  altering  the  conditions  of  ex- 
periment, laid  upon  a  thick  pad  made  of  layers  of  filter-paper,  or 
on  a  sufficiently  heated  block  of  salt  clay,  an  opposite  reaction 
will  be  exhibited  with  equal  regularity,  with  both  bipolar  and 
unipolar  excitation,  since,  as  in  the  fresh  organ  in  situ,  the  make 
excitation  appears  at  the  anode,  the  break  excitation  at  the  kathode. 
It  is  clear  that  this  can  only  be  explained  by  differences  in  current- 
distribution.  If  the  thin  muscular  canal  of  the  ureter  is 
stretched  freely,  or  on  a  non-conducting  support,  the  current  will 
be  distributed  somewhat  according  to  Fig.  91  (after  Engelmann). 


ELECTRICAL  EXCITATION  OF  MUSCLE 


It  is  evident  that  if  the  make  excitation  occurs  only  at  the 
point  where  current  leaves  the  muscular  integument  (the  latter 
is  hatched  in  the  figure)  the  same  could,  and  indeed  must,  be 
the  case  in  the  proximity  of  the  positive  electrode  also.  "  If  the 
branches  of  current  drawn  in  the  figure  as  proceeding  from  E  + 
(the  anode)  are  followed,  it  will  be  noticed  that  a  part  of  them 
leave  the  muscle-substance  at  the  points  e'  e'  e'" .  These  points 
(secondary  kathodic  points)  lie  in  the  immediate  proximity  of  the 
positive  electrode,  but  are  of  course,  with  regard  to  the  muscle- 
substance,  to  be  viewed  as  the  negative  pole  (physiological  kathode). 
And  here  the  closure  excitation  makes  its  appearance."  That 
this  does  not  actually  occur,  is  referred  by  Engelmann  in  part  to 
the  differences  in  current  density  on  the  side  turned  towards,  and 
away  from,  the  electrode,  in  part  to  the  depression  of  excitability 
and  conductivity  of  the  contractile  substance  in  the  region  of  the 


Fig.  91. 


positive  electrode  {infra).  A  much  wider  distribution  of  the  lines 
of  current,  and  hence  a  richer  development  of  secondary  kathodic 
points  in  the  region  of  the  anode,  and  conversely  of  secondary 
anodic  points  in  the  region  of  the  kathode,  occurs,  however, 
invariably  whenever  the  ureter  is  left  in  situ,  or  placed  on  a 
moderately  good  conductor  (Fig.  92).  Conditions  being  favour- 
able, excitation  (contraction)  will  then  occur  on  closure  of  the 
current  at  innumerable  places  in  the  proximity  of  the  anode  (not 
at  the  anode  itself),  and  is  either  transmitted  as  an  undulation 
(ureter),  or  remains  localised  as  a  persistent  contraction.  Con- 
versely, further  diffusion  of  the  closure — excitation  discharged 
at  the  kathode  proper  is  hindered  by  the  vicinity  of  secondary 
anodic  points. 

It  can  hardly  be  necessary  to  point  out  that  these  considera- 
tions are  legitimate  and  valid  in  all  the  cases  previously  quoted, 
where,  as  in  the  muscles  of  Holothuria  and  Echinidae,  and  also 
the  muscular  integument  of  worms,  and  the  intestine  of  verte- 


256 


ELECTRO-PHYSIOLOGY 


brates,  the  conditions  required  for  a  wider  distribution  of  lines  of 
current  in  the  proximity  of  the  electrodes,  and  therewith  also  for 
the  effectuation  of  secondary  electrodes,  are  aijriori  and  unavoidably 
present.  The  conspicuous  thickness  of  all  these  parts  is  the  reason 
that  the  lines  of  current  do  not,  even  with  bipolar  excitation,  adjust 
themselves  (as  in  the  exposed  nerve,  or  ureter)  mainly  in  a  direction 
parallel  with  the  long  axis  of  the  organ,  between  the  two  points  in 
contact  with  the  electrodes,  but  that  there  is  inevitably  a  further 
distribution,  and,  so  to  speak,  diffusion,  of  the  current  in  the 
proximity  of  the  point  where  it  enters,  as  well  as  that  where  it 
leaves,  the  muscle.  The  most  important  result  of  these  experi- 
ments, in  various  parts  of  smooth  muscular  organs,  is  undoubtedly 


Fig.  92. 


the  fact  that  in  conformity  ivith  the  laiu  of  -polar  excitation,  as 
established  for  striated  muscle,  the  make  excitation  is  without  excep- 
tion discharged  at  the  p)hysiological  kathode  only,  i.e.  the  true  point 
of  exit  of  current  from  the  contractile  suhstance  of  the  entire 
muscle,  and  is  seldom  transmitted  heyond  this  point;  while, 
on  the  other  hand,  excitation  never  ap)p)ears  at  the  physiological 
anode  itself  on  closure  of  the  circuit,  hut  ruhere  a  state  of  tonic  con- 
traction is  present,  local  inhibition  of  the  existing  excitability  may 
appear  as  a  more  or  less  obvious  localised  relaxation  of  the  muscular 
tissue,  followed  occasioncdly ,  lohen  the  current  is  opened,  by  a  contraction 
which  in  extension  and  character  exactly  reseinbles  the  i^o^^istent 
kathodic  closure  contraction.  While  this  last  nearly  cdways  appears 
as  a  tolercdaly  well-defined  sioelling,  a  ^^(^'i'sistcnt  closure  contraction 
of  qiiite  a  different  character  may  often  be  seen  on  both  sides  of  the 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  257 

anode,  extending  over  a  large  area ;  in  individual  cases  {intestine, 
muscidar  integument  of  ivorms,  ureter)  this  gives  the  in^yression  that 
the  mcdce  excitcdion  proceeds  entirely  and  chiefly  from  the  anode,  a, 
vieio  that  has  already  been  expressed  hy  Jofh  with  regard  to  the 
intestine  (34). 

It  may  be  questioned  if  there  is  any  analogue  to  this  reaction 
in  striated  skeletal  muscle.  But  before  entering  on  this  dis- 
cussion, it  will  be  advisable  to  go  a  little  more  closely  into  the 
allied,  and  from  various  points  of  view  highly  interesting,  pheno- 
mena in  cardiac  muscle  (35).  Since  the  heart  alternates  rhythmic- 
ally between  contraction  and  relaxation,  we  are  able  to  test  the 
action  of  the  current  in  both  phases.  It  is  advisable  to  use  the 
heart  of  a  cold-blooded  animal,  beating  as  slowly  as  possible — e.g.  a 
large  and  well-cooled  frog.  If  two  line  brush  electrodes  are  then 
applied  to  the  surface  of  the  ventricle  at  two  parts  as  wide  apart 
as  possible,  with  persistent  closure  of  a  sufficiently  strong  battery 
current,  a  very  striking  result  will  ensue.  At  each  new  systolic 
contraction  a  local  relaxation  of  the  ventricle  appears  at  the 
anode  during  closure  of  the  current,  in  the  form  of  a  dark- 
red,  blistered  swelling  ;  while  on  opening  the  current,  on 
the  other  hand,  the  kathodic  area  is  invariably  first  to  relax 
during  one  or  several  systoles,  presenting  an  appearance  exactly 
similar  to  the  anode  during  closure.  These  manifestations  can 
be  still  better  investigated  with  the  unipolar  method  of  excita- 
tion, one  unpolarisable  brush  electrode  being  placed  on  any  indif- 
ferent point,  e.g.  the  skin  of  the  throat,  while  the  other,  a  finely 
pointed  contact,  is  applied  to  the  ventricle,  in  such  a  way  that 
the  circuit  is  never  interrupted  while  the  heart  is  in  motion,  with- 
out undue  pressure.  The  effects  vary  according  to  the  strength  and 
direction  of  the  current,  and  the  condition  of  the  heart-muscle  at  the 
moment  of  excitation.  If  the  current  enters  by  the  electrode  in 
contact  with  the  ventricle,  and  closure  is  effected  at  the  beginning 
of  the  systole,  the  first  result  of  weak  excitation  (1  Dan.,  rheochord 
resistance  20,  or  more)  will  regularly  be  relaxation  at  the 
point  of  contact  and  its  immediate  proximity,  repeated  at 
each  new  systolic  contraction  as  long  as  closure  of  the  current 
continues.  "With  increasing  intensity  of  current  there  is  a  corre- 
sponding increase  in  the  degree  and  amplitude  of  the  relaxation, 
which  at  first  is  strictly  local,  standing  out  from  the  pale,  con- 
tracted, surrounding  area  as  a  little  red  speck,  scarcely  1  mm.  in 

s 


258  ELECTRO-PHYSIOLOGY 


diameter.  This  grows  more  and  more  prominent  as  a  congested 
expansion  of  the  muscular  wall  of  the  ventricle,  spreading  with 
comparative  rapidity  on  all  sides  beyond  the  region  of  prunary 
relaxation.  As  Schiff  correctly  observes,  with  reference  to  the 
analogous  effect  of  local,  mechanical  excitation,  the  diastolic 
relaxation,  after  attaining  a  certain  amplitude,  sometimes  appears 
to  stand  still  for  "  a  brief  period,"  and  then  spreads  slowly  over 
the  whole  ventricle. 

In  other  cases,  however,  we  have  observed  as  unmistakably, 
particularly  in  much  cooled,  slowly -beating  hearts  (which  are 
used  by  preference  in  all  these  experiments),  that  the  diastolic 
wave  spreads  with  uniform  rapidity  from  the  seat  of  initial 
relaxation  at  the  anode  over  the  entire  ventricle.  Exactly  the 
same  effects  as  appear  in  the  contracted  ventricle  at  the  anode,  on 
closure  of  a  constant  current,  occur  unmistakably  at  the  kathode 
immediately  after  the  circuit  is  opened. 

If  with  the  same  experimental  conditions  the  current  is 
reversed  without  moving  the  electrodes,  it  will  be  seen  at  break — 
given  adequate  intensity  and  duration  of  current — that  at  the 
moment  of  most  pronounced  systolic  contraction  the  previously 
anodic,  but  now  kathodic,  part  of  the  ventricle  is  always  the 
first  to  relax  itself  The  diffusion  of  the  originally  local  diastole 
increases  again  with  the  strength  of  current,  but  a  second  and 
no  less  important  factor  here  comes  into  play,  i.e.  the  duration 
of  closure  of  the  existing  current.  Up  to  a  certain  point  a  longer 
period  of  closure  of  a  weak  current  can  be  substituted  for  the 
action  of  stronger  currents.  Stronger  currents,  however,  are 
always  required  a  j^riori  to  produce  the  kathodic  opening  as 
plainly  as  the  anodic  closure  relaxation.  The  polar  phenomena 
of  relaxation  thus  described  in  the  ventricle  of  the  frog's  heart 
contracted  in  systole  may  be  very  elegantly  demonstrated,  if  the 
two  finely-pointed  thread,  or  brush,  electrodes  are  placed  at  two 
points  on  the  upper  surface  of  the  ventricle  as  far  apart  as  possible 
in  the  longitudinal  or  transverse  direction,  with  tolerably  pro- 
longed closure  of  a  not  too  weak  current.  During  the  period  of 
closure  a  local  diastole  occurs  at  the  anode  with  each  new  sys- 
tolic contraction.  At  break  of  the  current  the  relations  are 
inverted,  and  for  two,  or  even  several,  successive  systoles  the 
kathodic  region  is  the  first  to  relax. 

If  it  were  possible  to  keep  the  frog's  heart  for  long  in  con- 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  259 

tinuous  systolic  contraction,  the  sole  visible  effects  of  electrical 
excitation  with  the  constant  current  would  be  local  relaxation  of 
the  muscular  wall  of  the  ventricle,  appearing  with  closure  at  the 
anode,  but  with  opening  at  the  kathode — thus,  as  it  were,  forming 
an  antithesis  to  the  response  of  the  muscle  relaxed  in  diastole. 
It  is  difficult,  and  more  or  less  incidental,  to  obtain  a  prolonged 
systolic  contraction  in  the  frog's  heart ;  but,  on  the  other  hand, 
this  is  easily  produced  in  the  cardiac  muscle  of  many  invertebrates, 
e.g.  snail's  heart  (35).  We  have  already  seen  that  a  ventricle  tied 
to  a  canula  will  often,  if  the  latter  is  suddenly  filled  with  fluid 
(snail's  blood,  0*6  %  NaCl),  fall,  after  a  longer  or  shorter  series  of 
regular  contractions,  into  a  state  of  protracted,  uniform  contraction. 
If  during  this  time  a  current  of  1—2  Dan.  is  led  through  it 
by  means  of  unpolarisable  electrodes,  by  allowing  the  suitably- 
moistened  thread  of  the  lower  ligature  of  the  apex  of  the  heart 
to  dip  into  a  vessel  with  salt  solution,  in  which  one  of  the  elec- 
trodes is  already  plunged,  while  the  other  pointed  brush  electrode 
is  placed  above  the  second  ligature  at  the  boundary  between 
auricle  and  ventricle,  an  immediate  relaxation  of  the  ventricle 
may  be  seen  in  every  case  with  closure  of  the  circuit,  which 
however — it  must  be  noted — never  occurs  simultaneously  at  all 
points  of  the  area  traversed,  but  begins  without  exception  at  the 
end  where  current  enters,  i.e.  at  the  anode.  The  relaxation 
always  progresses  in  the  direction  of  the  current  from  the  positive 
to  the  negative  pole,  and  forms  a  more  or  less  rapidly-transmitted 
wave,  always,  however,  visible  to  the  eye.  If  the  current  is  only 
kept  closed  until  the  "wave  of  relaxation  "  has  reached  the  kathodic 
end  of  the  preparation,  and  is  then  broken,  the  ventricle  returns 
as  a  rule — at  least  in  all  cases  where  the  tonus  was  at  initio 
strongly  developed — to  its  original  state  of  continuous  contrac- 
tion. It  is  only  in  cases  where  a  less  pronounced  tonus  prevails 
from  the  beginning  of  the  experiment,  or  where  the  preparation 
is  excited  at  a  time  when  the  pulsations  have  begun  again  spon- 
taneously, that  an  unbroken  series  of  regular,  rhythmical  contrac- 
tions follow  a  single  short  closure  of  the  constant  current,  in 
which  case  they  either  persist  indefinitely  or  give  way  after  a  time 
to  secondary  tonic  contraction.  In  many  cases  the  ventricle 
remains  for  several  seconds,  during  the  closure  of  the  current,  in 
a  state  of  diastolic  relaxation,  after  which  only  it  begins  the  rhyth- 
mical peristaltic  contractions.      The  anodic  relaxation  frequently 


260  ELECTRO-PHYSIOLOGY 


occurs  more  readily  at  one  than  at  the  other  end  of  the  pre- 
paration, and  as  a  rule  the  base  of  the  ventricle  appears  most 
favourable  in  this  respect.  This  is  probably  related  to  the  fact 
stated  above,  that  the  mechanical  stimulus  of  the  ligature  often 
produces  a  pronounced  local  contraction  at  the  apex  of  the  heart, 
which,  as  was  also  pointed  out,  opposes  much  greater  resistance 
to  the  action  of  the  anode  than  the  tonic  contraction  produced 
by  the  state  of  wall-tension. 

If  the  electrodes  are  placed  at  opposite  ends  of  the  transverse 
axis  of  the  ventricle,  relaxation  will  begin,  on  closing  the  current, 
at  the  side  of  the  anode,  and  accordingly  the  heart  bulges  out  on 
the  same  side. 

The  intensity  of  current  at  which  these  phenomena 
appear  is  essentially  dependent  upon  the  strength  of  the  exist- 
ing "  tonus."  We  have  frequently  obtained  marked  effects  on 
using  a  Daniell  cell,  with  rheochord  resistance  from  a  wire  of 
5  cm.,  and  it  may  be  taken  as  a  general  rule  that  with  experi- 
mental conditions  as  described  above,  anodic  relaxation  rarely 
fails  with  a  resistance  of  100  cm.  wire.  If  only  minimal 
currents  are  employed,  the  relaxation  is  always  confined  to  the 
close  proximity  of  the  point  where  the  current  enters.  It  appears 
at  closure,  and  gradually  disappears,  even  if  the  exciting  current 
remains  closed.  In  other  cases  it  spreads,  according  to  the 
direction  of  the  current,  over  one  or  the  other  half  of  the 
ventricle.  With  moderate  currents,  and  great  excitability  of  the 
preparation,  the  propagation  of  the  anodic  wave  over  the  entire 
ventricle  is  independent  of  whether  the  current  is  broken  imme- 
diately after  the  effect  appears,  or  whether  it  remains  closed  for  a 
longer  period.  In  the  last  case,  however,  the  rhythmical  contrac- 
tions continue  during  the  whole  period  of  closure,  and  it  should 
be  noted  that  with  each  new  diastole,  relaxation  invariably  begins 
at  the  anode,  and  progresses  from  that  point  peristaltically. 
Hence,  by  merely  watching  the  pulsations  of  a  snail's  heart,  under 
the  influence  of  the  constant  current,  the  direction  of  the  current 
may  be  accurately  determined. 

The  systolic  contraction  of  the  ventricle  follows  so  much  more 
rapidly  that  mere  inspection  will  not  suffice  to  determine  whether 
under  these  conditions  it  also  proceeds  peristaltically  (starting 
from  the  kathode),  or  not. 

As  previously  stated,  the  rate  of  propagation  of  the  anodic 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  261 

wave  of  relaxation  is  so  slow  that  its  progress  may  conveniently 
be  followed  with  the  eye.  For  the  rest  it  varies  considerably. 
"While  in  one  case  the  wave  requires  several  seconds  to  spread 
over  the  small  tract  implicated,  averaging  5  to  7  mm.,  in  other 
cases  a  fraction  of  a  second  will  be  sufficient.  This,  again,  depends 
essentially  upon  the  degree  of  tonus  present,  and  one  might  say 
that  the  more  pronounced  this  is,  the  slower  will  be  the  diffusion 
of  relaxation  from  its  starting-point.  If  the  excitation  is  repeated 
with  unchanged  direction  of  current,  or  if  the  current  is  left 
closed,  it  is  easy  to  see  that  the  rate  of  propagation  of  the  anodic 
wave  increases  in  time  up  to  a  certain  value — which  it  soon 
reaches ;  if  the  current  is  reversed  it  diminishes  again  quickly. 

The  period  of  latent  excitation,  generally  speaking,  varies  in 
the  same  sense.  The  relaxation  at  the  anode,  as  is  immediately 
evident,  never  begins  precisely  at  the  moment  of  closure  of  the 
current,  but  is  always  preceptibly,  often  considerably,  later,  so 
that  a  latent  period  of  one  or  more  seconds  is  by  no  means  rare. 
In  many  cases  it  may  be  shorter,  but  is  never  so  brief  that  it 
cannot  be  detected  directly  by  the  eye. 

If  the  experiment  is  made  with  preparations,  which  ah 
initio  exhibit  a  marked  degree  of  tonic  contraction,  the  relaxa- 
tion starting  from  the  anode  appears  to  be  the  sole  visible  effect  of 
the  current,  a  previous  increase  of  contraction  under  such  circum- 
stances being  at  all  events  imperceptible.  That  such  increase 
is,  however,  present  under  certain  conditions  of  relaxation, 
may  be  ascertained  in  all  cases  in  which  there  is  primarily 
only  a  medium  degree  of  tonic  contraction.  For  then,  with 
closure  of  an  adequate  current,  the  ventricle  may  be  seen  to  con- 
tract in  the  first  place  simultaneously,  in  all  its  parts,  after  which 
only  the  peristaltic  relaxation  from  the  anode  commences. 

If  the  contraction  in  this  case  proceeds  from  the  kathode,  as 
may  be  affirmed  on  the  strength  of  experiments  to  be  described 
later,  the  conclusion  which  appears  from  the  reaction  is  that 
the  latent  period  of  the  kathodic  closure  excitation  is  smaller, 
while  the  rapidity  of  transmission  is  more  rapid,  than  in  anodic 
closure.  On  the  other  hand,  the  latter  seems  to  take  effect  at 
a  lower  intensity  of  current,  e.g.  we  have  repeatedly  found, 
with  a  weak  tonus,  that  a  (local)  relaxation  began  earlier, 
i.e.  with  less  rheochord  resistance,  than  in  the  closure  contraction 
in  question. 


262  ELECTRO-PHYSIOLOGY 


Engelmann  showed  that  every  Httle  muscle -bridge  which 
unites  two  otherwise  separate  parts  of  the  frog's  ventricle,  effects 
a  physiological  process  of  conductivity  between  them,  inasmuch 
as  the  excitation  coming  from  the  auricle  is  carried  through  the 
bridges  to  the  lower  portion  of  the  ventricle.  There  is  thus  a 
conductivity  of  excitation  from  cell  to  cell  without  any  inter- 
position of  nervous  elements.  Similarly  it  may  be  shown  that 
the  anodic  wave  of  relaxation  is  propagated  from  one  half  of  the 
ventricle  to  the  other,  if  any  minute  portion  of  the  normal  mus- 
cular wall  remains  to  establish  connection.  By  carefully  pinching 
the  side  of  an  anodically  relaxed  ventricle  of  a  large  snail's  heart 
with  small  forceps,  it  is  easy  to  make  the  greater  part  of  its  wall 
in  the  middle  section  incapable  of  conducting.  When  subse- 
quently traversed  by  current,  relaxation  can  be  seen  to  pass  over 
the  small  conducting  bridges,  although  far  more  slowly  than  under 
normal  conditions. 

A  contusion  extending  right  over  the  middle  part  of  the 
ventricle,  and  dividing  it  into  two  excitable  halves  separated 
by  a  small,  unexcitable  zone,  affords  a  means  of  investigating 
the  phenomena  which  appear  on  excitation  with  the  constant 
current  more  exactly  than  is  possible  in  the  entire  uninjured 
heart.  The  experiment,  indeed,  presents  certain  difficulties,  since, 
owing  to  the  great  sensibility  of  the  preparation  to  mechanical 
excitation,  the  two  halves  of  the  ventricle  are  not  seldom  un- 
equal in  their  capacity  for  response,  one  or  other  of  them  remain- 
ing more  distinctly  contracted,  or,  at  all  events,  not  returning 
to  the  relaxed  state ;  but  notwithstanding  this,  a  little  practice 
will  generally  obtain  the  desired  result — provided  the  animals  are 
large  enough.  If  such  a  preparation  is  traversed  by  a  battery 
current  of  sufficient  strength,  we  see — as  is  to  be  expected — that 
only  the  anodic  half  relaxes,  while  the  kathodic  either  exhibits 
no  changes,  or  contracts  distinctly  on  closure  of  the  current  if  its 
tonus  is  but  little  apparent.  On  opening  the  circuit  this  reaction 
is  exactly  reversed  in  favourable  instances ;  the  kathodic  section 
of  the  ventricle  relaxes,  while  the  anodic  goes  into  contraction. 
It  should  be  noted  that  both  halves  of  the  ventricle  have  their 
physiological  anode  and  kathode.  That,  notwithstanding  this,  an 
effect  can  be  detected  upon  one  side  only,  is  necessarily  due  to 
the  fact  that  the  density  of  current  is  less,  on  the  one  hand,  at 
the  point  of  injury  (owing  to  the  larger  section),  while,  on  the 


in  ELECTRICAL  EXCITATION  OF  MUSCLE  263 

other,  there  is  injury  to  the  muscle-substance,  caused  by  mechani- 
cal impact. 

Especially  remarkable  in  this  method  of  experiment  is  the 
relaxation  immediately  consequent  on  break  of  current  at  the 
effective  kathode ;  it  can  in  no  respect  be  distinguished  from 
the  anodic  closure  relaxation,  and,  as  we  shall  see,  must  in  all 
probability  be  regarded  as  an  equivalent  process. 

"With  regard  to  time,  the  order  of  succession  of  these  pheno- 
mena is  that  the  kathodic  half  contracts  immediately  upon 
closure,  after  which  the  anode  begins  to  relax.  Similarly,  on 
opening  the  anodic  break  excitation,  characterised  by  a  strong 
rapid  contraction  of  the  section  of  ventricle  affected,  the 
kathodic  opening  effect  follows,  and — like  the  anodic  make  — 
produces  relaxation  of  the  previously  contracted  parts.  There 
is  thus  a  coincidence  between  the  effects  of  the  kathodic 
make  and  anodic  break  excitation  on  the  one  hand,  and  the 
anodic  make  and  kathodic  break  on  the  other. 

It  is  important  to  the  significance  of  the  kathodic  opening 
relaxation  to  observe  it  at  its  best  upon  fresh,  excitable  prepara- 
tions, and  in  a  few  successive  makes  or  breaks  only.  The  effect 
grows  weaker  and  more  obscure  in  proportion  with  the  length  of 
closure,  or  frequency  of  stimulation,  with  uniform  direction  and 
strength  of  current,  and  finally  it  fails  altogether.  Whatever 
means  of  excitation  may  be  employed,  we  have  observed 
this  to  be  especially  conspicuous  in  certain  cases  where, 
after  double  ligaturing  of  the  apex  of  the  heart,  resulting  in 
pronounced  contraction,  the  effect  occurred  on  one  side  only 
with  subsequent  passage  of  current.  The  entire  descending 
current  of  a  Daniell  cell  produced  in  this  case  a  marl^ed  (anodic) 
relaxation  at  the  base  of  the  otherwise  uninjured  ventricle, 
extending  only  over  a  very  small  portion  of  it.  Closure  of 
the  ascending  current  produced  no  effect,  or  at  most  resulted  in 
a  weak  contraction  of  the  previously  relaxed  upper  section,  while, 
on  the  other  hand,  after  a  prolonged  closure  of  about  4  sees.,  the 
kathodic  opening  relaxation  appeared  at  the  base  with  great  dis- 
tinctness, though  only  in  a  few  consecutive  excitations.  Having 
once  become  aware  of  this  effect,  we  repeatedly  obtained  the 
same  result  on  the  normal  heart  immediately  after  attach- 
ing the  canula,  when  the  tonic  contraction  had  developed 
itself.     Two  conditions  are  here  essential :  first,  the  preparation 


264  ELECTRO-PHYSIOLOGY  chap. 

must  be  fresh,  and  as  excitable  as  possible ;  second,  the  current 
must  not  be  too  weak,  nor  closed  for  too  brief  a  period.  As  a 
rule,  2  to  3  sees,  closure  was  sufficient  with  the  full  strength  of  a 
Daniell  cell.  After  the  first  anodic  wave  of  relaxation  has  run  out, 
the  ventricle  contracts  in  systole,  next  a  peristaltic  diastole  sets  in, 
and  so  forth.  If  the  current  is  broken  shortly  after  the  second 
or  third  systole  has  begun,  a  diastolic  wave,  beginning  at  the 
kathode,  may  frequently  be  seen  to  sweep  over  the  entire 
ventricle,  i.e.  diametrically  opposite  to  the  former  direction. 
Sometimes  this  may  still  be  detected  in  the  second  and  even 
third  diastole  after  the  current  has  been  opened,  followed  at  the 
point  of  peristaltic  relaxation,  if  the  pulsations  continue,  by  a 
diastole  which  seems  to  commence  simultaneously  all  over  the 
ventricle.  From  this  we  may  infer  that  the  kathodic  break,  like 
the  anodic  make,  relaxation,  propagates  itself  from  cell  to  cell 
(by  conductivity)  from  its  starting  -  point.  This  conclusion, 
together  with  the  fact  that  the  first-named  effect  only  occurs 
plainly  under  the  most  favourable  conditions,  seems  to  exclude 
the  hypothesis  that  it  is  a  manifestation  of  fatigue,  produced  by 
persistent  kathodic  excitation.  It  is  much  more  probable  that  we 
are  here  in  face  of  a  characteristic  and  active  reaction  (equivalent 
to  the  anodic  closure  eff'ect)  of  tonically  contracted  cardiac 
muscle. 

These  facts  relating  to  the  effect  of  the  electrical  current 
upon  the  cardiac  muscle  of  invertebrate  and  vertebrate  animals 
may  no  less  appropriately  arrest  our  attention  than  the  excitation 
effects  previously  described  in  smooth  muscle,  since  they  form  a 
distinct  contribution  to  our  knowledge  of  the  effects  of  the 
electrical  current.  We  see,  in  the  first  place,  that  the  kathodic 
make  and  anodic  break  contraction  are  by  no  means  the  only 
visible  effects  of  electrical  excitation,  but  that  an  antagonistic 
inhibitory  effect  also  occurs  occasionally  during  an  existing  state 
of  excitation,  and  expresses  itself  as  the  relaxation  of  a  pre- 
viously contracted  part.  Since,  in  the  great  majority  of  cases 
relating  to  the  electrical  excitation  of  contractile  structures, 
the  latter  are  in  a  state  of  comparative  quiescence  at  the  moment 
of  excitation,  it  is  intelligible  that  nearly  all  observations 
should  refer  to  those  manifestations  of  activity  which  it  has 
alone  been  usual  to  regard  as  excitation  phenomena.  But  the 
investigation    of    appropriate    objects    further     shows    that    the 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  265 

electrical  current,  of  which  the  direct  and  normal  effect  is 
contraction  of  the  relaxed  and  "  resting "  muscle,  is  able  no 
less  legitimately  to  inhibit  a  pre-existing  excitation,  and  to  pro- 
duce an  active  relaxation  of  the  contracted  muscle.  It  may 
further  be  demonstrated  that  these  "  inhibitory  effects "  of  the 
current  cause  true  "  polar  effects  "  just  as  much  as  the  excitatory 
process,  and  as  in  this  last  two  "  excitations,"  distinct  with 
regard  to  time  and  place,  if  otherwise  equivalent,  may  be  dis- 
tinguished as  the  closing  and  opening  excitation,  so  here  it  seems 
justifiable  in  the  cases  cited  to  speak  of  two  equally  distinct 
"  inhibitions,"  a  closing  and  an  opening  inhibition,  or,  more 
properly,  anodic  and  kathodic  inhibition,  inasmuch  as  the  one 
appears  at  the  point  of  entrance,  the  other  at  the  point  of 
exit  of  the  current.  It  was  to  be  expected  a  i^riori  from  the 
complete  coincidence  in  physiological  properties  between  cardiac 
and  skeletal  muscle-fibres,  that  under  favourable  conditions  there 
should  be  polar  effects  of  inhibition  at  the  latter  also. 

It  is  evident  that,  in  order  to  decide  this  question,  a 
suitable  muscle  must  be  thrown  into  a  state  of  persistent  excita- 
tion, comparable  with  that  of  cardiac  muscle  during  systolic  con- 
traction, or  during  the  characteristic  "  tonus  "  of  the  snail's  heart. 
This  is  best  effected  by  the  use  of  veratrin,  which,  as  has  been  said, 
so  changes  the  muscle-substance  that  after  a  short  impact  of  stimu- 
lation there  is  not,  as  under  normal  conditions,  a  rapid  twitch,  but  a 
prolonged  tonic  contraction,  often  persisting  unchanged  for  several 
seconds,  during  which  period  the  effects  of  the  electrical  current 
can  be  conveniently  studied  (36).  We  have  found  it  advisable 
to  introduce  6  to  7  drops  of  acetate  of  veratrin  (1  %  solution)  into 
the  posterior  lymph -sac  of  a  frog,  which  was  killed  about  ten 
minutes  later.  The  typical  curve  of  contraction  of  a  muscle  thus 
poisoned  (sartorius)  has  already  been  described.  It  is  only 
necessary  to  recall  the  effect  observed  when  a  muscle,  fixed  in 
the  middle,  and  extended  in  Bering's  double  myograph,  and 
excited  by  a  single  induction  shock,  is  traversed,  after  the  maxi- 
mum of  contraction  has  been  reached,  by  a  battery  current,  pre- 
ferably ascending.  The  anodic  half  of  the  muscle  will  then,  at 
the  moment  of  closure,  lengthen  considerably,  and  the  correspond- 
ing curve  makes  a  sudden  drop,  while  the  kathodic  half,  as  a 
rule,  becomes  more  contracted  at  the  same  moment,  or  at  any 
rate    shows   no   longitudinal   changes.      If   the   current   is    then 


266  ELECTRO-PHYSIOLOGY  chap. 

opened  after  a  short  closure,  diametrically  opposed  changes  of 
form  will  be  visible  in  favourable  cases  in  both  halves  of  the 
muscle.  The  anodic  half  shortens,  often  in  no  inconsiderable 
degree,  which  must  obviously  be  the  expression  of  the  break 
excitation,  while  at  the  same  time  the  kathodic  half  is  more 
plainly  relaxed  than  would  presumably  have  been  the  case  without 
the  intervention  of  excitation.  On  rapidly  repeating  the  stimuli, 
with  uniform  direction  of  current,  the  same  phenomena  ap- 
pear, though  in  diminishing  quantity,  as  at  the  beginning  of 
the  excitation,  for  as  long  a  period  as  the  muscle  remains  in  any 


Fig.  93. — Sartorins  fixed  in  the  middle  (double  myograph).  Persistent  veratrin  contraction.  S, 
closure ;  0,  opening  of  a  constant  current.  Relaxation  occurs  at  the  anodic  (A),  con- 
traction at  the  kathodic  (A"),  half  of  the  muscle. 

considerable  contraction  (Fig.  93).  From  this  it  would  seem 
that  we  are  here  concerned  essentially  with  local  changes  in  the 
muscle,  confined  to  the  immediate  proximity  of  the  physiological 
anode  or  kathode,  and  not,  as  in  cardiac  muscle,  extending 
over  a  larger  area.  The  changes  of  form  described  above 
in  the  sartorius,  thrown  by  veratrin  into  an  artificial  state 
"  analogous  to  tonus,"  present  a  complete  analogy  with  the 
consequences  of  electrical  excitation  in  systolically- contracted 
cardiac  muscle,  as  above  described.  Here,  too,  along  with  the 
ordinary  effects  of  polar  excitation  (which  for  the  rest  appear  less 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  267 

plainly  than  during  the  resting  condition,  and  may  even  fail 
altogether),  polar  inhibitory  effects  may  be  directly  demonstrated, 
and  express  themselves  in  the  quelling,  or  diminution,  of  a  pre- 
viously existing  state  of  excitation,  and  in  a  relaxation  conditioned 
by  the  same,  which  is  in  the  first  place  local.  The  well-known 
leng-thening;,  at  closure  of  a  homodromous  current,  of  the  muscle 
in  persistent  opening  contraction  must  be  regarded  as  a  kindred 
phenomenon,  preserving  a  distinctive  character  only  in  so  far  as 
in  this  case  there  is  inhibition  of  the  state  of  excitation  produced 
by  the  after-effects  of  the  previous  current  at  the  physiological 
anode.  Since  a  kathodic  break  inhibition  may  also  be  demon- 
strated, at  least  incipiently,  upon  the  veratrinised  muscle,  where 
the  curve  in  question  drops  suddenly,  the  hypothesis  of  two 
inhibitory  processes,  antagonistic  to  the  polar  excitatory  processes 
(which  do  not,  as  a  rule,  find  visible  expression  in  striated  skeletal 
muscle,  while  in  many  smooth  muscles,  as  also  in  cardiac  muscle, 
they  are  easily  demonstrable  during  systolic  contraction),  would 
appear  to  be  perfectly  justified. 

A  few  points  still  remain  for  consideration,  i.e.  certain 
phenomena  which  may  appear  at  closure  during  the  electrical 
excitation  of  striated  muscle,  and  are  obviously  analogous  to  the 
excitation  phenomena  appearing  at  the  anode  in  many  smooth 
muscles.  In  both  cases  the  effect  is  due  solely  to  the  appearance 
of  secondary  kathodic  points.  We  have  already  seen  that  in  the 
longitudinally  traversed  sartorius  (fixed  by  the  middle  clamp) 
there  is  frequently,  with  strong  ascending  currents,  a  well- 
marked  persistent  closure  contraction  in  the  anodic  half 
of  the  preparation  also,  which  cannot  be  referred  to  an  en- 
croachment of  the  persistent  K.C.C.^  This  is  most  plainly 
seen  with  injury  (death)  of  the  kathodic  end.  In  this  case  even 
very  strong,  admortal  currents  {i.e.  directed  towards  the  demarca- 
tion surface)  fail  to  produce  any  trace  of  continuous  contraction 
at  the  limit  of  demarcation,  although  the  muscle  twitches  sharply 
upon  closure  of  the  circuit ;  on  the  other  hand,  there  is  invari- 
ably a  continuous  contraction  at  the  anodic  end  of  the  muscle, 
which   increases    directly   with   the    strength    of    current.      This 

^  A. C. C.  =  Anodic  closure  contraction. 
A.O.C.  =  Anodic  opening  contraction. 
K.C.C.  =  Kathodic  closure  contraction. 
K.O.C.  =  Kathodic  opening  cG^ntraction. 


268 


ELECTRO-PHYSIOLOGY 


effect  is  unmistakable  to  the  unaided  eye,  or  with  a  magnifying 
lens,  but  with  the  graphic  method  many  additional  details  can  be 
detected.  If  a  sartorius  (stretched  in  the  double  myograph, 
killed  at  the  pelvic  end,  and  clamped  in  the  middle)  is  excited 
by  currents  of  increasing  strength  (4—8  Dan.,  with  rheochord), 
the  first  effect  produced  will  be  only  the  normal  reaction  of 
muscle  injured  at  one  end,  as  described  already.  Excitation 
with  a  descending  current  is  followed  by  a  pronounced  make 
twitch  (fairly  symmetrical  in  both  halves  of  the  muscle),  with  a 
subsequent  persistent  contraction,  which  appears  in  the  kathodic 
half  only.  The  closure  of  the  ascending  current  is  at  first  with- 
out any  effect,  even  at  such  a  strength  of  current  as  would  in 
the  normal  muscle  provoke  maximal  closure  contractions  under 
the  same  conditions.  Beyond  a  certain  limit  of  intensity,  how- 
ever, the  ascending  (admortal)  current  once  more  begins  to  excite 
at  closure,  often  indeed  before  an  effective  break  excitation 
appears  with  the  same  direction  of  current  under  conditions 
favourable  to  its  development,  because  the  current  is  of  greater 
density  at  its  exit  from  the  small  end  of  the  muscle. 

The  make  excita- 
tion always  expresses 
itself  at  first  as  a 
pronounced  twitch  on 
the  anodic  side  with- 
out any  conspicuous 
persistent  contrac- 
tion. With  increased 
strength  of  current, 
however,  this  appears 
also,  exclusively  in  the 
anodic  hcdf  of  the 
muscle ;  the  kathodic 
hcdf  relaxes  completely  after  the  make  twitch  has  sid)sided  (Fig.  94). 
At  a  certain  strength  of  current  the  latter  nearly  always 
overtops  the  twitch  at  closure  of  the  descending  ("  abmortal ") 
current.  With  increasing  current  intensity,  the  persistent  A.C.C. 
increases  rapidly  at  the  lower  end  of  the  muscle,  and  in  its  turn 
soon  exceeds  the  persistent  K.C.C.  of  the  descending  current  in 
magnitude  and  extension  (Fig.  94). 

In  addition  to  this,  the-  gradual  swelling  of  the  persistent 


Fig.  94. — Sartorius  fixed  at  the  middle,  killed  at  the  pelvic 
eiid(O).  (8  Dan.)  Persistent  anodic  closure  contraction. 
After  a  pause  of  twelve  minutes  the  effect  of  the  de- 
scending make  excitation  (at  V)  had  decreased  consider- 
ably, while  the  ascending  excitation  remained  uniform. 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  269 

A.C.C.  with  repeated  excitation  is  very  noticeable.  There  is 
little  doubt — as  could  easily  be  verified  experimentally  by  time- 
measurements — that  the  closing  twitch  in  a  parallel-fibred  muscle 
killed  at  one  end  is  discharged  with  a  sufficiently  strong  ad- 
mortal  current  in  the  anodic  half  of  the  muscle,  from  whence  it  is 
propagated  outwards.  This  appears,  inter  alia,  from  the  fact  that 
under  these  conditions  the  curve  of  the  twitch  on  the  anodic  side 
is  considerably  larger  than  that  at  the  kathode,  while  in  all  cases 
where  excitation  starts  from  the  kathode  alone,  the  corresponding 
half  of  the  muscle  is  most  strongly  contracted. 

Direct  observation  of  the  anodic  end  of  the  muscle,  preferably 
with  the  magnifying  lens  after  previous  banding  with  sepia,  shows 
that  the  persistent  anodic  contraction  which  appears  with  closure 
of  strong  currents,  extends,  unlike  the  well-marked  persistent 
K.C.C.,  over  a  fairly  large  area,  never,  however,  producing,  as  in 
that  case,  a  swelling  at  the  exterior  ends  of  the  fibres,  which  are, 
indeed,  rather  extended  visibly,  i.e.  are  unexcited.  The  two  or 
three  most  internal  bands  of  sepia,  as  well  as  the  uncoloured 
spaces  between  them,  do  not  perceptibly  decrease  or  approximate 
(as  is  characteristic  at  the  kathodic  end),  whereas,  on  the  contrary, 
the  more  central  bands  do  decrease  and  draw  tooether,  curving; 
conversely  towards  the  anode.  This  leads  to  a  contraction  swell- 
ing, starting  from  the  continuity  of  the  muscle,  but  close  to  the 
anodic  end,  and  gradually  dying  out  towards  the  middle.  If  one 
electrode  (kathode)  is  applied  to  one  of  the  two  bone  stumps  of 
the  sartorius,  while  the  finely-pointed  anode  is  in  contact  with 
any  point  of  the  surface  of  the  moderately  extended  muscle,  it  is 
apparent,  even  with  weak  currents  (2—3  Dan.),  that  there  is  no 
trace  of  contraction  at  the  actual  point  of  entrance,  and  with  sepia 
marking  it  is  easy  to  see  that  at  such  a  point  there  is  a  not 
inconsiderable  extension  of  fibres, — as  appears  plainly  in  a  corre- 
sponding expansion  of  the  cross -band  in  contact  with  the 
electrode,  as  well  as  in  the  adjacent  segment  of  fibres.  This 
passive  extension  at  the  entrance  of  the  current  is  caused  by  a 
more  or  less  pronounced  contraction,  which  originates  at  both 
sides  of  the  anode  at  closure,  and  persists  during  the  passage  of 
the  current.  By  this  method  of  experiment  it  is  possible  to 
observe  the  local  anodic  inhibition  (relaxation)  of  the  veratrin 
muscle  more  easily  and  plainly  than  with  the  above-described 
graphic  method.      It  is  only  necessary  to  close  the  circuit  twice 


270  ELECTRO-PHYSIOLOGY 


in  succession  without  disturbing  the  electrodes :  first,  for  a 
moment  only,  to  produce  sustained  contraction  of  the  vera- 
trinised  sartorius ;  and  secondly,  for  longer,  in  order  to  observe 
the  local  relaxation  at  the  anode. 

If  the  normal  muscle  in  situ  is  stimulated  with  unipolar 
excitation,  the  difference  between  kathodic  and  anodic  effects  is 
strongly  marked,  even  with  the  weakest  currents.  While  with 
punctiform  contact  of  the  muscle  surface  with  the  kathode,  a 
local  persistent  contraction  appears  at  the  point  of  contact  only, 
(after  the  make  twitch  has  subsided),  while  the  rest  of  the  surface 
remains  perfectly  even,  stimulation  with  the  anode  produces — in 
consequence  of  the  persistent  excitation  in  the  bundles  of  fibres 
on  either  side  of  the  point  at  which  current  enters — a  deep, 
permanent,  longitudinal  furrow  upon  the  surface  of  the  muscle, 
while  the  actual  point  of  contact  and  its  immediate  neighbourhood 
remains  unexcited,  and  more  or  less  extended,  so  that  a  flat, 
dinted  constriction  appears. 

With  this  mode  of  excitation  the  break  effect  shows  very 
plainly  as  a  small  swelling,  which  appears  at  the  point  where  the 
current  enters,  as  soon  as  the  circuit  is  broken,  and  remains 
visible  for  a  long  period.  The  similarity  between  this  re- 
action in  striated  skeletal  muscle,  and  the  effects  of  electrical 
excitation  in  smooth  muscle  discussed  above,  is  undeniable,  so 
that  the  presumption  of  a  fundamental  uniformity  in  the  response 
of  these  two  kinds  of  muscle,  as  well  as  of  cardiac  muscle,  to  the 
electrical  current,  can  hardly  be  disputed.  This  applies  both  to 
the  manifestations  of  polar  excitation,  and  the  equally  polar 
effects  of  inhibition.  When  it  is  remembered  that  the  manifesta- 
tions of  excitation  near  the  anode  only  appear  with  weak 
currents,  on  "  unipolar "  excitation,  and,  as  found  from  recent 
experiments,  fail  altogether  if  the  muscle  (sartorius)  dips 
into  fluid,  and  is  longitudinally  traversed — appearing  only 
at  a  high  intensity  of  current,  notably  when  the  direction  is 
ascending,  if  the  preparation  is  stretched  in  Hering's  double 
myograph — it  can  hardly  be  doubted  that  we  are  again  in  face  of 
excitation  effects  at  secondary  kathodic  points,  the  existence  of 
which,  with  unipolar  excitation,  is  self-evident,  but  which  must 
also  be  present,  more  particularly  at  the  knee  end  of  the 
sartorius,  when  current  is  sent  in  from  the  stumps  of  bone  behind 
it.     This  is  the  necessary  consequence  of  the  peculiarly  graduated 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  271 

fibre-endings  at  this  end  of  the  muscle,  which  provide  repeated 
opportunities  for  the  current  to  escape  into  adjacent  fibres  of 
the  muscle. 

Although  these  phenomena  are  of  no  special  physiological 
interest,  they  are  deserving  of  thorough  investigation,  on  account 
of  the  very  striking  polar  effects — due  to  the  same  causes — in 
different  smooth  muscular  organs,  which  might  easily  conduce  to 
the  fallacious  assumption  that  there  was  a  reversal  of  Pfliiger's 
law  of  excitation.  On  the  other  hand,  we  find  in  them  the 
key  to  a  number  of  older  observations  on  striated  muscle. 
Even  the  earlier  literature  contains  some — if  rare — instances, 
which  indicate  that  striated  muscle,  under  certain  conditions, 
if  not  invariably,  exhibits  a  reaction  to  the  electrical  current 
which  differs  from  the  normal,  inasmuch  as  at  closure  of  the 
current,  excitation  appears  on  the  anodic  side  also.  The  first 
observations  in  this  connection  are  those  of  Aeby  (20),  dating 
from  1867,  which  led  him,  in  opposition  to  Bezold  and  Engelmann, 
to  the  conception  of  a  h'qjolar,  though  unequal  excitation  of  the 
muscle,  by  the  constant  current.  Moreover,  Aeby  thought  he  had 
proved  that  under  certain  conditions,  more  particularly  with 
progressive  fatigue  of  the  preparation,  the  normal  reaction — in 
which  the  excitatory  action  of  the  kathode  far  exceeds  that  of 
the  anode — was  exactly  reversed.  Aeby's  experiments,  however, 
are  by  no  means  unimpeachable,  as  both  Engelmann  and 
Hering  (1)  pointed  out  later.  This  applies  in  particular  to  an 
experiment  in  which  the  two  legs  of  a  frog  still  united  by,  and 
dependent  from,  the  pelvis,  are  traversed  by  current,  the  two  wires 
used  as  electrodes  being  connected  to  the  lower  end  of  the  legs. 
The  bones  of  the  thigh  were  previously  freed,  and  on  excitation 
the  leg  traversed  in  a  descending  direction  appeared  to  contract 
more  markedly  than  that  in  which  the  current  passed  upwards, 
from  which  Aeby  concluded  that  the  effect  at  the  negative  pole 
predominated.  But  no  account  is  taken,  on  the  one  hand  of  the 
difference  between  physical  and  physiological  electrode  points,  as 
insisted  on  by  Engelmann  and  Hering ;  on  the  other  hand,  of  the 
difference  in  density  of  current  at  knee  end  and  pelvic  end  of 
the  two  limbs  respectively.  Still,  however,  even  in  this  case  the 
reversal  of  effect  becomes  apparent  after  prolonged  duration  of 
experiment.  Aeby  concludes  from  this  that  fatigued  and  dying 
muscle  possesses  different  properties  from  fresh  muscle ;  it  is  no 


272  ELECTRO-PHYSIOLOGY 


longer  excited  to  greater  activity  at  the  negative,  but  only  at 
the  positive,  pole.  Engelmann,  also,  came  to  the  conclusion  later 
that  such  a  complete  reversal  of  phenomena  (i.e.  of  the  law 
of  polar  excitation)  might  take  place.  But  until  it  has  been 
determined  by  unexceptional  experiments,  there  must  be  great 
scepticism  in  regard  to  such  statements. 

Aeby  also  set  up  experiments  in  which  a  single  muscle 
(sartorius,  adductor  magnus)  was  fixed  at  the  middle  with  a 
clamp,  so  that  both  halves  moved  freely.  By  reversing  the 
direction  of  current  the  twitch  of  one  (the  lower)  half  only  was 
graphically  recorded.  "  At  the  closing  twitch  more  energy  was 
invariably  developed  at  the  negative  than  at  the  positive  pole,  in 
a  fresh  muscle  "  ;  with  very  weak  currents  the  kathodic  half  only 
contracted.  The  break  twitch  usually  behaves  conversely  to  the 
make  twitch.  Engelmann  is  inclined  to  refer  this  effect  to  the 
disturbance  of  conductivity  at  the  clamped  part,  whence  it 
would  follow  that,  e.g.  at  closure,  the  excitation  starting  from 
the  kathode  cannot  propagate  itself  without  diminution  to 
the  anodic  side.  Here,  again,  however,  Aeby's  conclusion 
"  that  the  negative  twitch  suffers  much  more  from  fatigue 
than  the  positive,"  and  that  with  much  fatigue  the  reaction 
of  the  fresh  muscle  may  be  inverted,  appears  to  be  of  value. 
The  preceding  observations  on  the  clamped  sartorius  might  easily 
be  recorded  as  a  further  confirmation  of  Aeby's  conclusions  (cf 
Fig.  94),  but  the  phenomena  in  question  only  appear  character- 
istically with  such  strong  currents  that  the  effectuation  of 
secondary  kathodic,  or  anodic,  points  is  not  thereby  excluded, 
and  may,  even  in  Aeby's  experiments,  have  played  a  considerable 
part. 

In  conclusion,  we  must  not  omit  the  much  talked -of 
alterations — hitherto  investigated  by  the  pathologist  only — 
which  appear  after  the  peripheral  paralysis  of  striated  (warm- 
blooded) muscles,  in  regard  to  electrical  reaction.  These,  as  pre- 
viously stated,  express  themselves  partly  in  quantitative  changes 
of  excitability  towards  induced  and  constant  currents,  partly,  as 
will  be  shown,  by  a  qualitative  alteration  of  the  polar  effects  of 
excitation,  and  that  in  the  direction  stated  above  for  Aeby's 
fatigued  muscle.  While,  under  normal  conditions,  the  kathodic 
efiect  of  excitation  (so-called  "  kathodic  closure  twitch ")  pre- 
ponderates    considerably    in    direct     unipolar     excitation     of    a 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  273 

muscle  by  the  constant  current,  this  ratio  is  reversed  in 
paralysed  inuscles  at  a  certain  degree  of  degeneration  ("  reaction 
of  degeneration ").  Before  giving  a  final  judgment  it  would  be 
necessary  here,  as  in  fatigued  muscle,  to  make  further  investiga- 
tions with  unassailable  methods,  for  _  the  conditions  under 
which  alone  the  experiments  in  question  can  be  tried  in  man,  or 
have  been  tried  on  other  animals,  by  no  means  correspond 
with  the  demands  of  an  exact  physiological  method.  On  the  other 
side,  there  are  so  many  results,  derived  from  irreproachable  ex- 
periments upon  different  muscles  and  nerves,  which  are  opposed 
to  the  theory  of  a  reversal  of  polar  effects,  that  any  supposed 
exception  must  a  priori  encounter  suspicion,  and  can  only  hope 
for  recognition  if  the  conditions  of  experiment  and  all  accessories 
are  perfectly  simple  and  obvious. 

Among  the  visible  manifestations  of  excitation  which  appear 
in  striated  muscle,  in  consequence  of  the  electrical  current,  must 
be  reckoned  the  so-called  Porrefs  effect  or  galvanic  muscle-tvave. 
Kiihne  (37),  in  1860,  first  described  this  remarkable  appearance. 
A  muscle  with  parallel  fibres,  traversed  by  a  strong  current,  falls 
into  a  characteristic  wave-like,  or  flowing,  movement,  which 
spreads  in  the  direction  of  .  the  positive  current,  and  remains 
localised  to  the  intrapolar  area.  Kiihne  only  alludes  tentatively 
to  a  possible  connection  of  this  appearance  with  the  Eeuss-Porret 
phenomenon  of  electric  transfusion,  but,  on  the  other  hand,  he 
expressly  points  out  the  "  deep  internal  relation  to  what,  with 
electrical  excitation,  is  termed  a  twitch."  Du  Bois-Eeymond  (38) 
also  recorded  this  wave  as  an  excitation  effect,  the  expression 
of  localised  contraction  proceeding  from  anode  to  kathode.  The 
whole  appearance,  indeed,  recalls  in  a  marked  degree  the  fine 
waves  and  ripples  which  sometimes  appear  in  the  frog's  sartorius 
with  mechanical  excitation  also,  and  show  directly  that  "  the 
wave  is  a  form  of  muscular  motion,  which  can  arise  luithout  any 
excitation  hy  current."  Undoubtedly,  waves  of  contraction  of  very 
different  heights  may  spread  over  the  muscle ;  "  at  one  moment  they 
are  enormously  expanded,  at  the  next  so  fine  that  to  the  naked 
eye  they  only  appear  as  a  delicate  ripple ;  sometimes  they  run  in 
the  single  bundles  cpiite  independently  of  one  another,  so  that 
many  swellings  can  be  seen  to  spread  simultaneously  in  different 
directions  ;  sometimes  a  single  swelling  extends  itself  over  a  larger 
area  of  the  muscle  surface"  (Hermann,  39, p.  603).     The  velocity 

T 


274  ELECTRO-PHYSIOLOGY 


of  the  wave  varies  considerably,  but  is  always  insignificant. 
Hermann  {I.e.)  estimates  it  in  fresh,  freely-undulating  prepara- 
tions at  4  to  5  mm.  per  sec.  We  have  already  shown  that  toler- 
ably strong  currents  are  necessary  in  order  to  produce  a  clear 
effect.  It  is  fundamental  to  the  conception  of  the  wave  as  an 
excitation  phenomenon  that  it  is  exclusively  charaeterutic  of 
striated  living  muscle,  and  is  non-existent  in  other  moist  tissues ;  ^ 
further,  as  Hermann  showed  {l.c),  an  effect  of  fatigue  and  re- 
covery of  the  muscle  may  be  demonstrated,  since  the  energy  and 
rapidity  of  the  wave  diminish  gradually,  to  increase  again  after  a 
prolonged  period  of  quiescence.  Above  all,  however,  it  must  be 
noted  that,  as  in  muscular  excitation  in  general,  the  temperature 
of  the  moment  affects  the  galvanic  wave  in  a  most  striking  maMner. 
On  sending  current  through  fresh  muscles  (sartorius)  in  a  warm 
oil  bath,  Hermann  (I.e.)  found  that  the  effect  appeared  in 
extreme  perfection,  no  idea  of  which  could  be  formed  from 
ordinary  experiments.  The  diffusion,  as  well  as  the  height  and 
velocity  of  the  wave,  are  enormously  increased  by  higher  tem- 
perature ;  on  the  other  hand,  the  effect  disappears  entirely 
with  even  moderate  cooling.  The  effect  of  muscular  tension  is 
further  very  conspicuous.  The  wave  is  always  most  marked 
with  the  ordinary  medium  degree  of  tension,  and  ceases  to  be 
visible  with  either  very  high,  or  completely  absent,  tension. 
When  the  significance  of  the  degree  of  tension  at  any  given 
moment  to  muscular  excitation  (as  also  to  metabolism)  in  the 
entire  muscle  is  remembered,  this  reaction  can  hardly  be  sur- 
prising. 

It  has  already  been  shown  that  the  direction  of  the  wave  is 
always  from  anode  to  kathode,  but  the  anode  itself  is  not  the 
starting -2)oint  of  the  vxtvcs  of  contraction.  If  excitation  is  effected 
with  a  current  of  such  intensity  that  the  wave  is  just  perceptible, 
it  appears,  as  a  rule,  to  be  most  marked  in  that  tract  of  the 
muscle  which,  during  closure,  is  thrown  into  persistent  contraction. 
It  frequently  happens  that  the  extreme  ends  of  the  fibres  on  the 
anodic  side,  as  also  the  entire  kathodic  half  of  the  muscle,  show 
no  trace  of  the  wave,  while  the  greater  part  of  the  anodic  side  is 

1  On  applying  strong  currents  Neumann  (12)  frequently  observed  a  phenomenon 
in  cardiac  muscle  (of  frog)  which  appears  to  be  analogous  with  the  galvanic  wave,  in- 
asmuch as  peristaltic  waves  spread  during  closure  in  the  direction  of  the  current  in 
such  regular  succession  "  that  the  heart  seems  to  give  faint,  delicate  pulsations." 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  275 

thrown  into  pronounced  undulation.  Invariahlij,  hoivcver,  the 
luave  begins  in  the  immediate  jyroximiti/  of  the  anodic  end  of  the 
muscle,  and  spreads  thence  in  marked  currents  over  the  entire 
muscle.  This  points  to  a  very  close  relation  between  the 
above-described  persistent  anodic  closure  contraction  and  the 
"  galvanic  wave,"  and  it  can  hardly  be  fallacious  to  regard  both 
phenomena  as  two  different  symptoms  of  one  and  the  same 
change  in  the  muscle.  In  this  connection  it  is  to  be  noted 
that  Hermann  (I.e.  p.  602)  occasionally  received  the  impression 
that  on  opening  the  circuit  "a  short  ripple  or  wave  proceeded 
towards  the  anode — i.e.  in  the  opposite  direction  to  the  character- 
istic phenomenon."  Death  or  chemical  change  at  the  end  of  the 
muscle  produced  as  little  effect  upon  the  galvanic  wave  as  upon 
the  persistent  anodic  closure  contraction.  If  this  last  is  admitted 
to  be  a  manifestation  of  excitation  depending  upon  the  effectuation 
of  secondary  electrode  points  in  the  continuity  of  the  muscle 
traversed  by  the  current,  the  galvanic  wave  can  hardly  be 
regarded  as  different.  In  ^iew  of  these  results,  the  theory 
supported  mainly  by  Jendrassik  (40)  and  Eegeczy  (41)  that  the 
galvanic  wave  is  principally  due  to  the  changes  of  form  and 
place  which  the  canaliculi  containing  blood  and  lymph  in  the 
entire  muscle  (or  any  part  of  it  which  consists  of  several  bundles) 
undergo  in  consequence  of  the  endosmotic  transference  of  fluid 
particles  within  them,  caused  by  the  constant  current,  must  be 
regarded  as  sufticiently  contradicted,  especially  as — since  Her- 
mann's researches — there  can  be  no  doubt  as  to  the  active 
co-operation  of  the  living  and  excitable  muscle-fibres.  Hermann's 
explanation  (I.e.)  of  the  galvanic  wave,  on  the  other  hand,  presents 
no  objections.  He  starts  from  the  unquestionably  correct 
assumption  that  with  even  the  strictest  longitudinal  excitation  of 
a  muscle  with  parallel  fibres,  "  the  majority  of  fibres  have  not 
merely  one  anodic  and  one  kathodic  point,  corresponding  with  the 
electrodes  of  the  entire  muscle,  but  a  great  number  of  points  of 
entrance  and  exit,  due  to  the  oblique  or  transverse  course  of  the 
lines  of  current  to  single  points  of  the  fibres,  especially  where 
the  latter  are  accidentally  crumpled  together."  Strong  currents 
set  up  excitation  at  each  of  the  secondary  kathodic  points,  by 
which  a  contraction  swelling  is  produced,  that  spreads  slowly 
towards  the  kathode.  "  The  origin  and  progress  of  the  swelling 
makes  new  changes  and  new  irregularities  between  the  lines  of 


276  ELECTRO-PHYSIOLOGY 


current  and  the  fibres,  and  thus  new  excitation  is  occasioned.  In 
this  wise  the  marvellous  wave  can  be  accounted  for."  Special 
attention,  however,  must  be  given,  on  the  one  hand  to  the  starting- 
point  of  the  wave,  and  on  the  other  to  the  difficulty  already  pointed 
out  by  Hermann,  that  the  wave  fails  to  appear  just  when,  as  it 
seems,  all  the  conditions  are  most  favourable  to  the  production 
of  secondary  kathodes  by  curvature  of  the  fibres,  i.e.  in  completely 
relaxed  muscle.  If  it  is  admitted,  as  Hermann  states,  that  under 
certain  conditions  of  zig-zag  curvature  in  the  muscle,  the  physio- 
logical effect  of  longitudinal  passage  of  current  may  be  equivalent 
to  that  of  purely  transverse  current — since  in  the  one  case,  as 
in  the  other,  the  anode  and  kathode  of  the  same  fibre  are 
exactly  opposite — it  must  also  be  remarked  that  the  wave  is 
conspicuously  absent  in  many  cases,  where  curvature  of  the  fibres 
can  hardly  be  detected  in  the  extended  muscle.  In  order  to 
explain  the  slow  propagation  of  the  waves  of  contraction  (in  one 
direction  only),  Hermann  assumes  that  there  is  injury  to  con- 
ductivity within  the  entire  intrapolar  area,  in  consequence  of 
excitation  by  strong  currents.  This,  however,  seems  question- 
able when  we  reflect  that  a  perfectly  similar  wave  may  also  be 
observed  independently  of  the  imssage  of  current  in  quite  fresh 
muscle,  if  it  is  excited  in  a  given  way  (mechanically).  It  was 
shown  above  that  the  same  muscle  may  transmit  slow  and  fast 
waves  of  contraction,  without  any  considerable  underlying  altera- 
tion in  its  condition.  It  is  due  far  more  to  the  quality  of  the 
stimulus. 

It  is  very  essential  to  the  entire  theory  of  these  mani- 
festations of  excitation  in  the  continuity  of  the  muscle  (as  to  which 
there  is  still  much  to  be  explained)  that  we  should  know 
whether  the  electrical  current  does  not  produce  further  change 
within  the  area  of  muscle  traversed,  in  addition  to  the  polar 
effects  described,  or  whether — as  has,  so  far,  been  tacitly  accepted 
— this  tract  is  only  indirectly  affected  by  the  action  set  up  at  the 
most  important  physiological  points  of  anode  and  kathode.  Here 
there  is  of  course  no  question  of  the  temporary  effectuation  of 
secondary  electrode  points.  Von  Bezold  (10),  to  whom  we  owe 
the  first  thorough  investigation  into  the  electrical  excitation  of 
denervated  muscle,  included  this  question  in  his  experimental 
inquiries,  and  replied  to  it  by  saying  that,  so  long  as  current 
traversed  the  muscle  at  constant  strength,  there  were  continuous 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  277 

physiological  changes  in  the  entire  area  traversed,  by  which,  on 
the  one  hand,  the  excitability,  and  on  the  other,  the  conductivity, 
of  the  intrapolar  tract  were  fvmdamentally  affected.  Since 
changes  in  the  excitability,  or  conductivity,  of  any  section  of 
the  muscle  can  only  be  inferred  indirectly  from  corresponding 
changes  in  the  magnitude  of  contraction,  observed  at  the  same 
spot  with  uniform  excitation,  the  main  point  in  the  case  before 
us  is  to  apply  uniform  stimuli  to  any  point  of  the  intrapolar 
tract,  before,  during,  and  after  the  passage  of  current,  and  then 
to  measure  the  height  of  twitch  by  graphic  methods.  It  is 
obvious  that  only  the  electrical  stimulus  is  applicable  in  this 
case,  since  it  alone  permits  of  exact  graduation  of  the  strength, 
and  does  no  immediate  injury  beyond  the  spot  excited.  But  the 
application  of  the  electrical  current  as  a  test  stimulus  of  the 
excitability  of  a  tract  of  muscle  already  traversed  by  current,  has 
to  contend  with  considerable  practical  difficulties  on  account  of 
the  hardly  avoidable  interference  of  the  two  currents.  If  the 
battery  current,  the  effect  of  which  is  to  alter  the  excitability 
and  conductivity  of  the  tract  of  the  muscle  traversed,  is  termed 
the  "  polarising,"  while  the  induction  current,  on  the  other  hand, 
used  as  the  test  stimulus,  is  called  the  "  exciting,''  current,  it  is 
clear  that  if  the  electrodes  of  the  latter  are  applied  directly  to 
the  muscle  traversed  by  the  constant  current,  current  must 
necessarily  ilow  from  the  one  circuit  into  the  other  in  proportion 
with  the  resistance  in  both  circuits.  But  if  the  polarising  (con- 
stant) current  is  partly  diverted  into  the  circuit  of  the  exciting 
(test)  current,  a  physiological  kathode  will  necessarily  be  formed 
at  one  of  the  exciting  electrodes,  thereby  producing  a  continuous 
state  of  excitation,  which,  on  its  side,  complicates  the  effects  of 
the  test  stimulus,  so  that  temporary  changes  in  the  height  of  the 
twitch  produced  by  the  test  stimulus  before  and  after  closure  of 
the  polarising  current,  cannot  well  be  referred  to  alteration  of 
excitability  in  the  parts  in  question,  which  would  be  iiidc- 
IK'ndent  of  direct  excitation  by  the  polarising  current.  The 
following  point  must,  moreover,  be  taken  into  consideration. 

According  to  the  law  of  polar  excitation,  stimulation  takes  place 
— following  the  direction  of  the  current — now  at  one,  and 
now  at  the  other,  end  of  the  tract  traversed,  on  closure  of  the 
test  current,  from  which  it  necessarily  follows,  owing  to  the 
oblique    direction    of    the    lines    of    current    (from    the    lateral 


278  ELECTRO-PHYSIOLOGY 


situation  of  the  electrodes),  that  the  physiological  kathode,  or 
anode,  must  possess  a  considerable  extension.  In  the  one  case, 
therefore,  if  a  branch  of  the  polarising  current  diverges  into  the 
exciting  circuit,  the  physiological  kathode  of  the  test  current 
falls  upon  points  of  fibres  that  are  already  kathodic ;  at  other 
times  the  contrary  occurs,  since  the  kathode  of  the  test  current 
then  coincides  with  anodic  points.  The  effect  of  the  test  current 
naturally  depends  npon  its  direction.  Since  the  distribution  of 
current  into  the  two  circuits  depends  solely  upon  the  ratio  of 
resistance,  it  is  possible,  in  any  given  case,  to  throw  such  a  resist- 
ance into  the  exciting  circuit  that  the  resistance  of  the  short  tract 
of  muscle  between  the  corresponding  electrodes  shall  be  minimal, 
to  avoid  a  branching  of  the  constant  current  into  the  exciting 
circuit  (Hermann,  Handh.  II.  i.  p.  44).  The  experiment  is 
arranged  as  follows :  Two  non-polarisable  electrodes  fastened 
to  a  movable  holder,  are  applied  in  the  usual  manner  to  different 
points  of  a  sartorius,  stretched  in  Bering's  double  myograph. 
The  make  induction  current  is  exclusively  used  as  the  test 
stimulus,  and  is  led  in  by  threads  moistened  with  physiological 
NaCl  solution,  in  order  to  interfere  as  little  as  possible  with  the 
changes  of  form  in  the  muscle.  The  length  of  the  intrapolar 
tract  is  about  3  —  4  mm.,  and  its  resistance  is  therefore 
negligible  in  comparison  with  that  of  a  glass  tube  2  m.  long  by 
0'5  cm.  in  diameter,  filled  with  very  dilute  CuSO^  solution, 
introduced  into  the  primary  circuit.  The  twitches  are  recorded 
upon  a  smoked  surface,  one  electrode  of  the  double  myograph 
being  permanently  fixed,  while  the  other  is  in  connection  with 
a  writing-point.  The  intensity  of  the  polarising  battery  current 
is  graduated  as  required  by  a  rheochord.  The  closure  and 
opening  of  the  constant  current  is  effected  by  a  mercury  key 
introduced  between  the  rheochord  and  battery  (2  Dan.).  If  the 
polarising  and  exciting  current  have  the  same  direction  (both 
descending),  the  case  is,  in  the  first  place,  conceivable  in  which 
the  points  of  exit  fall  together,  the  negative  test  electrode  being 
applied  to  the  stump  of  the  tibia,  while  the  other  is  in  contact 
with  the  end  of  the  sartorius.  In  this  case  there  will  be  marked 
alterations  in  the  excitability  (to  be  described  below).  Quite 
other  results  occur,  when  both  exciting  electrodes  are  placed  in 
the  continuity  of  the  muscle.  According  to  v.  Bezold,  it  might 
be  expected  that  during  the  closure  of  a  very  weak  current,  a 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  279 

condition  of  increased  excitability  would  spread  from  the  kathodic 
end  over  a  certain  larger  or  smaller  area  of  the  tract  lying 
between  the  poles.  At  first  sight  this  seems  to  correspond  with 
the  observation  that  when  hotli  electrodes  are  so  applied  to  tlie 
lower  end  of  the  muscle  that  one  (kathode)  is  2  to  3  mm. 
away  from  the  tendon  end,  and  the  other  about  4  mm.  higher, 
the  height  of  the  minimal  twitch  discharged  by  the  closure  of  a 
descending  induction  current,  during  polarisation  by  a  very  weak 
descending  battery  current,  is  greater  than  it  was  before.  Closer 
examination,  however,  shows  that  this  conclusion  is  not  justified, 
the  experimental  result  being  due  solely  to  the  structure  of  the 
muscle.  Since,  i.e.  the  muscle-fibres  are  not  all  of  the  same 
length,  and  are  inserted  at  the  lower  end  into  an  oblique  surface, 
the  physiological  kathode  of  the  muscle  traversed  longitudinally 
in  a  downward  direction,  must  necessarily  extend  over  a  measur- 
able and  tolerably  extensive  portion  of  the  lower  half  of  the 
muscle.  So  long  therefore  as,  under  the  experimental  conditions 
described  above,  a  sufficient  number  of  ends  of  fibres  fall  under 
the  kathode  of  the  test  current,  a  perceptible  alteration  of  excita- 
tion effects  during  polarisation  —  manifesting  itself  either  as 
increase  or  as  diminution  of  excitability — is  perfectly  intelligible. 
The  latter,  i.e.  apparent  extension  of  depression  of  excitability 
over  the  intrapolar  muscle  region  may  be  observed  under  the 
same  experimental  conditions,  either  when  with  descending 
polarising  and  test  currents  the  intensity  of  the  former  increases, 
or  when  with  an  ascending  polarisation  current  the  exciting 
electrodes,  which  are  close  together,  are  brought  so  near  to  the 
lower  end  of  the  muscle  that  the  excitation  is  still  in  part  dis- 
charged within  the  anodic  area.  If,  however,  the  test  electrodes 
are  pushed  farther  and  farther  along  the  muscle  to  its  upper 
end,  it  may  easily  be  ascertained  that  with  the  given  strength 
of  the  polarising  battery  current  a  perceptible  change  in  the 
height  of  twitch  before  and  during  the  passage  of  current  cannot 
be  demonstrated  at  any  other  point  of  the  intrapolar  area.  It 
is  therefore  solely  the  spatial  distribution  of  the  points  of 
entrance  or  exit  of  current  at  the  lower  end  of  the  muscle,  due 
to  irregularities  of  structure  in  the  sartorius,  which  occasionally 
produce  a  wider  diffusion  of  the  excitatory  changes  confined, 
as  we  shall  see,  to  the  physiological  anode  and  kathode.  If 
the  negative  test  electrode  lies  outside  the  region  of  the  physio- 


280  ELECTRO-PHYSIOLOGY 


logical  kathode,  or  anode,  of  a  parallel-fibred  muscle  traversed 
longitudinally,  no  changes  of  excitability  will  be  displayed  in 
the  intrapolar  area,  in  either  a  negative  or  positive  sense, 
when  polarising  battery  currents  are  applied  of  not  excessive 
strength.  Just  as  little  would  this  be  the  case  at  break  of  the 
polarising  current.  It  would  thus  appear  that  the  electrical 
current  may  traverse  the  muscle  without  producing  any  directly 
demonstrable  alteration  of  the  substance  with  the  sole  exception 
of  the  polar  points.  Very  different,  as  we  have  seen,  is  the  re- 
action at  the  physiological  kathode  and  anode  proper.  Here  it  is 
easy  to  demonstrate  marked  changes  of  excitability  in  a  positive  or 
negative  direction,  either  resulting  from  a  pre-existing  persistent 
excitation,  or  as  the  after-effects  of  such,  or  caused  by  polar 
inhibitory  processes.  To  this  we  must  refer  the  observations  of 
V.  Bezold  on  alterations  of  excitability  in  the  tract  of  muscle 
traversed,  the  method  he  employed  being  only  adequate  to  test 
the  excitability  of  kathodic  and  anodic  points  of  fibres.  Start- 
ing with  the  presumption  that  an  induced  current  does  not, 
like  a  constant  current,  act  by  'polar  excitation  only,  but  that  it 
excites  all  points  of  the  area  traversed  simultaneously,  and 
uniformly,  v.  Bezold  endeavoured  to  test  the  so-called  "  total 
excitability "  of  the  tract  of  muscle  traversed  by  the  polarising 
battery  current,  by  making  use  of  a  break  induction  current  as 
test  stimulus,  led  into  the  muscle  by  the  same  electrodes  as  those 
which  conveyed  the  polarising  current.  Von  Bezold's  experiments 
may  be  represented  by  the  diagram  (Fig.  95). 

The  secondary  coil  of  an  induction  apparatus  (aS'.,)  is  intro- 
duced into  the  battery  circuit,  the  intensity  of  which  can  be 
regulated  by  a  rheochord.  If  the  constant  current  is  opened 
at  (a),  an  induction  current  will  traverse  the  muscle  in  one  or 
the  other  direction  at  closure  or  opening  of  the  primary  circuit, 
giving  rise  to  a  twitch  in  the  muscle.  If  the  battery  circuit 
is  closed  at  (a),  a  part  of  the  current,  at  any  given  intensity 
as  determined  by  the  rheochord,  will  pass  continuously  through 
the  muscle.  If  the  primary  circuit  is  again  made  or  broken, 
an  induced  current  of  the  same  strength  as  before  will  traverse 
the  now  polarised  muscle  in  the  corresponding  direction,  the 
relations  being  obviously  altered  only  in  so  far  as  the  exciting 
current  no  longer  starts  from,  and  returns  to,  a  density  of 
zero,    but    from   a    density    varying    with    the    strength    of   the 


ELECTRICAL  EXCITATION  OF  MUSCLE 


281 


polarising  current.  The  second  twitch,  like  the  first,  is  recorded 
graphically,  and  thus  we  obtain  a  comparative  tracing  of  the 
time-relations  and  magnitude  of  twitch  in  the  muscle  traversed 
(polarised),  or  not  traversed,  by  current.  If  v.  Bezold's  pre- 
sumption were  correct,  that  all  points  of  the  tract  through  which 
current  passes,  are  excited  simultaneously  and  uniformly,  the 
comparison  of  the  height  of  twitch  in  both  cases  would  not 
indeed  determine  the  changes  of  excitability  in  definite  points 
of  the   intrapolar    area,   since  the   different   elements   would    of 


Fig.  95. 

course  participate  collectively  in  such  changes,  each  according  to 
its  particular  state  at  the  moment;  but  we  should  obtain  the 
sum  of  resulting  excitability,  or  as  v.  Bezold  expresses  it,  the 
"  total  excitability,"  in  the  tract  of  muscle  traversed.  As,  how- 
ever, it  has  since  been  demonstrated  that  induced  currents,  like 
constant  currents,  have  only  polar  action,  the  experiments  de- 
scribed can,  of  course,  show  no  more  than  alterations  in  excita- 
bility at  the  physiological  kathode  or  anode.  It  is  therefore 
evident  that  v,  Bezold's  method  only  determines  the  alterations 
in    excitability   at    the   ends   of  the   fibres   in    a   longitudinally 


282 


ELECTRO-PHYSIOLOGY 


traversed  muscle,  and  contributes  nothing  in  regard  to  the 
excitability  of  the  intrapolar  region.  Besides  this  principal 
fallacy,  his  experiments  are  also  hampered  by  the  use  of  metal 
electrodes,  which  complicate  the  results  by  polarisation. 

In  order  to  determine  the  polar  excitoMlity  of  a  curarised 
muscle  with  parallel  fibres,  traversed  by  a  constant  current,  from 
the  above  method — with  as  few  fallacies  as  possible,  and  during  the 
])assage  of  the  current — the  uninjured  sartorius,  with  its  stumps  of 
bone  at  either  end,  must  be  attached  to  the  double  myograph 
with  unpolarisable  electrodes,  one  of  which  is  permanently  fixed, 
while  the  other  is  movable,  and  connected  with  a  writing  lever. 
The  arrangement  is  such  that  the  polarising  constant  current  and 
make  induction  current  traverse  the  muscle  in  the  same  ascending 
or  descending  direction. 

In  order  to  obtain  a  general  notion,  and  also  for  better 
comparison  with  the  results  of  v.  Bezold,  we  subjoin  two  out  of 
many  tables  of  results  in  which  the  same  method  is  followed  on 
the  whole  as  in  the  analogous  experiments  of  v.  Bezold : — 


9. 
10. 
11. 


Twitch.      Muscle  unpolarised 


5)  )5  .... 

Immediately  after  closure  of  very  weak  de- 
scending^ current  (2  Dan.  rheochord  res.  =  1) 

Immediately  after  breaking  this  current 

Muscle  unpolarised      .... 

Immediately  after  closure  of  strong  descending 
current  (res.  =  4)     . 

On  breaking  this  current 

Polarising  current  strengthened  (res.  =  8) 
immediately  after  closure 

3  sees,  later   ..... 

Immediately  after  opening  the  current 

1  minute  later  .... 


Height  of 
Twitch. 

4  mm. 

4     „ 

29     „ 

4     „ 
4     „. 

32  „ 
3     „ 

26  „ 
0  „ 
0  „ 
trace 


II. 

1.   Twitch.      Muscle  polarised  .  .  .  .  6  mm. 

2  6 

3.         ,,  Immediately  after  closure  of  weak  descending 

current  (2  Dan.  res.  =  1)       .  .  .  29     „ 


^  Descending  and  ascending  currents  vary  in  effect  because  of  the  asymmetrical 
form  of  the  sartorius. 


ELECTRICAL  EXCITATION  OF  MUSCLE 


283 


He 

gilt  of 

Twitch. 

4. 

Twitch. 

After  5  sees.  . 

• 

26 

mm. . 

5. 

)) 

)) 

7  sees,  more 

21 

6. 

5J 

5) 

4 

18 

7. 

5J 

J) 

4 

16 

8. 

5) 

)J 

4 

14 

9. 

» 

)5 

5 

8 

10. 

)> 

55 

5 

5 

11. 

>5 

55 

5           „ 

0 

12. 

5» 

55 

breaking 

the 

current 

0 

13. 

JJ 

55 

40  sees. 

0 

14. 

)) 

55 

50      „ 

3 

15. 

)? 

55 

62      „ 

5 

16. 

5) 

Immediately   after 

closure   of 

same   polarising 

ciirreut 

25 

17. 

)) 

5  sees,  later 

21 

18. 

>J 

5 

17 

19. 

3J 

5 

12 

20. 

)5 

5 

4 

21. 

5 

0 

It  is  obvious  from  these  tables  that,  as  v.  Bezold  found,  very 
weak  constant  currents  actually  increase  the  excitatory  effect  of 
single  induction  currents  sent  through  the  entire  intrapolar  area, 
provided  they  are  in  the  same  direction.  The  numbers  quoted 
show,  moreover,  that  the  increase  in  height  of  twitch  is  much 
more  significant  than  was  formerly  observed  by  v.  Bezold.  This 
is  in  great  measure  owing  to  the  fact  that  the  otherwise  unavoid- 
able and  rapid  decrease  of  intensity  in  the  weak  polarising  current 
is  prevented  by  the  use  of  unpolarisable  electrodes. 

An  essential  difference,  however,  between  these  results  and 
those  of  V.  Bezold  appears  when  the  effect  of  duration  of  current 
upon  the  consequences  of  test  excitation  are  taken  into  considera- 
tion. While,  i.e.  v.  Bezold  found  on  application  of  a  polarising 
current  that  the  height  of  the  twitch  discharged  by  an  induction 
shock  increased  perceptibly  with  the  duration  of  the  constant 
current  (notwithstanding  the  disadvantage  of  progressive  polarisa- 
tion from  the  metallic  electrodes),  we  have  never  experienced 
this.  Bather,  when  the  battery  current  was  at  first  of  very  loio  in- 
tensity, so  that  no  visible  sign  of  excitation  appeared  at  the  moment 
of  its  entrance  into  the  muscle,  the  height  of  the  augmented 
twitches  discharged  by  a  homodromous  induction  current,  did  not 
alter  perceptibly,  provided  the  polarising  current  was  not  closed 
for  too  long  a  period.      On  the  other  hand,  a  more  or  less  pro- 


284  ELECTRO-PHYSIOLOGY 


nounced  decrease  in  height  of  twitch  could  be  observed  in  the  latter 
case,  under  uniform  conditions.  It  is,  moreover,  unmistakable 
that  the  excitability  of  the  preparation  just  before  polarisation 
commences,  determines  the  time  in  which  the  diminution  of  ex- 
citability occurs  after  closure  of  the  constant  current.  As  a  rule 
it  may  be  said  that  depression  follows  the  period  of  heightened 
response,  in  the  kathodic  fibre  points  of  a  weakly-polarised  muscle, 
the  more  quickly  in  proportion  as  the  excitability  of  the  muscle 
is  ah  initio  lowered  from  any  cause,  local  or  general. 

This  is  exhibited  as  well  in  preparations  taken  from  frogs 
with  deficient  vitality,  as  in  those  in  which  excitability  is  only 
locally  diminished  (at  the  kathode)  by  the  temporary  passage  of 
current.  The  latter  effect  can  also  be  seen  in  Table  II.  of  the 
experimental  series.  Within  34  sees,  after  closure  of  the  weak 
polarising  current  the  augmentative  effect  of  the  homodromous 
make  induction  current  used  as  test  excitation — at  first  strongly 
marked — became  practically  zero.  So  soon  after  break  of  the 
constant  current  as  the  muscle  had  recovered  itself  sufficiently 
to  yield  distinct  twitches  with  the  same  test  as  before  the  first 
passage  of  current,  the  polarising  current  was  closed  again.  The 
height  of  twitch  immediately  reached  the  same  proportions  as  in 
the  first  series ;  on  the  other  hand,  the  excitability  of  the 
kathodic  points  of  fibres  diminished  much  more  quickly  than 
before,  since  a  passage  of  current  of  20  sees,  suffices  to  inhibit 
the  effect  of  the  same  stimulus.  The  depression  and  final  in- 
hibition of  previously  augmented  excitation  caused  by  a  homo- 
dromous induction  current,  makes  its  appearance  more  or  less 
quickly  in  proportion  with  the  intensity  of  the  battery  current 
sent  through  the  muscle. 

Starting  from  minimal  polarising  currents,  gradually  increased 
in  intensity  by  pushing  up  the  rheochord  slider,  and  giving  the 
muscle  time  to  recover  itself  between  each  pair  of  experiments, 
it  is  easy  to  verify  the  accuracy  of  this  last  statement.  At  a 
certain  intensity  of  current,  varying  in  proportion  with  the 
excitability  of  the  preparation,  the  increase  of  kathodic  response 
only  occurs  plainly  at  the  moment  immediately  consequent  on 
closure,  and  is  hardly  joerceptible  with  further  augmentation  of 
current  intensity.  This  does  not,  however,  as  might  be  concluded 
from  the  foregoing  observations  of  Engelmann  on  the  rabbit's 
ureter,  occur  for  the  first  time  when  the  constant  current  has 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  285 

already  produced  an  obvious,  persistent  K.C.C. ;  on  the  contrary, 
■  the  stage  of  augmented  response  in  most  cases  ehides  observa- 
tion (on  account  of  its  excessively  short  duration)  if  the 
intensity  of  the  polarising  current  is  insufficient  to  discharge  a 
maximal  closure  twitch  in  the  muscle.  It  is  therefore  a  universal 
principle  to  employ  only  the  weakest  battery  currents  when  the 
object  is  to  demonstrate  a  marked  increase  of  response  in  the 
kathodic  points  of  the  fibres  at  a  given  stage  of  polarisation, 
since  it  might  otherwise  be  easily  overlooked.  Hermann  (42), 
together  with  Pfliiger  and  Nasse  (in  older  experiments),  finds  that 
"  in  nerve,  as  well  as  in  muscle,  the  effect  of  a  given  induction 
current  is  increased  by  homodromous  constant  currents,  and  de- 
pressed (to  abolition)  by  opposite  currents."  Beginning  with  the 
weakest  constant  currents,  the  increase  of  excitation  from  homo- 
dromous variations  of  current  gives  way  to  diminution  when  the 
strength  of  the  constant  current  exceeds  a  certain  limit ;  Hermann 
obtained  the  same  results  in  a  still  more  unexceptional  manner 
by  using  battery  currents  for  excitation. 

In  Tables  I.  and  II.  {supra)  the  twitches  discharged  by  the 
test  stimulus  immediately  after  closure  of  the  battery  current 
were  approximately  maximal.  There  is  thus  an  a  priori  proba- 
bility which  receives  experimental  confirmation,  that  the  responsi- 
tivity  of  the  kathodic  points  of  fibres  in  a  muscle  traversed  l)y 
current  increases  up  to  a  certain  limit  with  the  intensity  of  the 
polarising  current.  This  limit,  however,  is  very  low ;  in  our  own 
experiments  it  was  reached  as  a  rule  at  1—2  cm.  deriving 
circuit,  with  2  Dan.  as  the  battery.  Beyond  this  limit,  excita- 
bility diminishes,  as  has  been  shown,  in  proportion  with  the 
strength  of  the  polarising  current. 

It  is  just  in  the  case  in  which  the  intensity  of  the  latter  is  so 
low  that  each  increase  of  it  produces  a  corresponding  augmentation 
of  the  excitatory  effect  of  a  homodromous  induction  current,  that 
the  increase  in  height  of  twitch  corresponding  to  increased  duration 
of  closure  of  the  battery  current,  recorded  by  v.  Bezold,  might  be 
expected ;  but  in  no  instance  has  it  made  its  appearance. 

What  conclusions  then  may  be  drawn  from  these  experiments  ? 
Since  we  know  that  the  induction  current  used  as  test  stimulus 
generally  produces  visible  excitation  at  the  kathode  only,  i.e.  at 
points  of  fibres  which,  during  the  closure  of  the  polarising 
current,  are  already  in  a  state  of  persistent  excitation,  the  con- 


286  ELECTRO-PHYSIOLOGY 


dition  of  excitability  at   the   kathode,  varying  as   it   does  with 
strengtli  and  duration  of  current,  must  be  regarded  solely  as  the  • 
consequence  of  localised  persistent  excitation,  and  the  question  is 
only  how  there  comes  to  be  sometimes  an  increase,  and  some- 
times a  depression,  of  excitability. 

It  must  be  admitted  that  the  electrical  current  traversino-  a 
muscle  acts  as  an  exciting  agent,  not  merely  at,  but  during  the 
whole  period  of  closure.  Further,  it  has  been  established  ex- 
perimentally, that  the  alterations  in  the  contractile  substance 
which  underlie  the  excitatory  process  are  confined  to  those  points 
of  fibres  by  which  the  current  leaves  the  muscle.  Each  experi- 
ment shows,  moreover,  that  the  appearance  of  a  make  twitch,  i.e. 
discharge  of  a  wave  of  excitation,  or  contraction,  at  the  point  of 
stimulation,  as  a  rule  implies  the  condition  that  the  oscillations 
of  current  from  zero,  or  any  finite  value,  should  occur  with  a 
certain  rapidity  ;  and  it  should  be  added  that  the  absolute 
intensity  of  the  excitation  current  also  must  surpass  a  given  limit, 
if  visible  manifestations  of  excitation  are  to  be  elicited.  Sup- 
posing that  a  muscle  is  persistently  traversed  by  a  battery 
current  of  such  low  intensity  that  its  presence  is  not  betrayed 
by  any  trace  of  visible  excitation,  we  are  none  the  less  justified 
in  assuming  that  a  "  latent  condition  of  excitation  "  is,  as  it  were, 
present  at  all  those  points  of  fibres  which  collectively  repre- 
sent the  "  physiological  kathode,"  during  the  passage  of  current ; 
for  that  altered  state  of  the  contractile  muscle-substance,  which, 
by  its  rapid  appearance  at  the  point  where  current  escapes,  sets 
up  a  wave  of  contraction  as  soon  as  the  intensity  of  the  current 
exceeds  a  given  minimal  limit,  and  the  continuance  of  which 
during  the  closure  of  stronger  currents  is  expressed  in  the  con- 
tinuous closure  contraction,  must  obviously  exist  on  closure  of 
the  weakest  currents  also,  albeit  in  a  lesser  degree. 

Only  a  small  sudden  increase,  greater  or  less  according  to 
circumstances,  will  then  be  required,  in  addition  to  the  constant 
but  inadequate  stimulus,  in  order  to  produce  a  wave  of 
excitation  at  the  kathode.  In  other  words,  a  rapid,  positive 
variation  of  a  very  weak  current  flowing  through  the  muscle 
may  effect  an  excitation,  even  when  the  same  variation,  starting 
from  zero  at  the  abscissa,  produces  no  effect,  or  only  minimal 
excitation  of  the  muscle.  The  increased  excitation  occasion- 
ally to   be    observed  with    an   induction   current,  homodromous 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  287 

with  the  polarising  battery  current,  may  therefore  be  explained 
as  the  summation  of  two  intrinsically  inadequate  stimuli,  and 
the  increased  response  at  the  kathode  appears  to  be  not  so 
much  a  peculiar  effect  of  current  introductory  to  the  excitatory 
process  as  the  actual  result  of  that  process.  This  theory  is  quite 
compatible  with  the  contradictory  behaviour  of  a  muscle  during, 
and  immediately  after,  protracted  weak  polarisation,  or  with  the 
application  of  stronger  currents. 

The  after-effects  observable  in  the  last  case  were  referred 
above  to  local  "  fatigue  "  of  the  kathodic  points  of  fibres,  induced 
by  current.  The  facts  before  us  show  that  almost  immediately 
after  closure  of  a  medium  current  there  is,  according  to  the 
duration  of  closure,  a  progressive  diminution,  or  even  complete  in- 
hibition, of  response  to  induction  currents  at  the  kathode.  The 
direct  dependence  of  the  depression  of  excitability  during  the 
passage  of  the  current  upon  its  duration,  with  low  polarisation 
intensity,  makes  it  highly  probable  that  in  this  case  the  excitatory 
process  itself,  or,  more  correctly  speaking,  the  fatigue  induced  by 
the  same  at  the  seat  of  direct  excitation,  must  be  regarded  as  the 
cause  of  the  decreased  response  at  the  kathode. 

The  protracted  condition  of  weak  excitation  at  the  kathode 
gradually  produces  alterations  in  the  contractile  substance  of  the 
muscle,  as  expressed  not  merely  during  closure  of  the  current, 
but  also  for  some  time  after  it  has  been  broken,  in  a  diminished 
excitability,  which  is  usually  explained  as  a  fatigue  effect.  It 
mast  be  asked,  however,  how  the  diminution  of  response  at 
the  kathode  immediately  after  the  closure  of  stronger  currents 
is  to  be  understood  and  explained.  Here  there  can  be  no  ques- 
tion of  "  fatigue  "  in  the  ordinary  sense  of  the  word,  because  no 
conspicuous  after-effect  outlasting  the  stimulus  can,  as  a  rule,  be 
demonstrated,  owing  to  the  brief  duration  of  closure. 

That  it  is  not  wholly  wanting  is  shown  by  the  fact  that  in  a 
series  of  twitches  produced  by  closing  the  constant  current  at 
short  intervals,  its  direction  remaining  unaltered,  the  height  of 
each  twitch  is  perceptibly  lower  than  that  which  immediately 
precedes  it ;  this  insignificant  after-effect  of  a  single  short  closure 
would  not,  however,  suffice  to  explain  the  continuously  marked 
depression  of  excitability  at  and  during  closure  of  the  same 
current.  An  induction  current  which  produces  maximal  twitches 
in  the  muscle  not  traversed  by  the  constant  current  is  totally 


288  ELECTRO-PHYSIOLOGY 


ineffective  during  the  passage  of  a  battery  current  of  medium 
intensity  in  the  same  direction,  while  it  recovers  its  former 
efficiency  in  full  as  soon  as  the  constant  current  is  broken. 

But  it  must  not  be  forgotten  that  even  the  excised  muscle 
possesses  a  large  capacity  of  recovery,  by  which  it  is  enabled  to 
equalise  the  changes  in  its  substance  caused  by  the  excitatory 
process  the  more  quickly  and  completely  in  proportion  as  the 
stimulus  acts  for  a  shorter  time,  or  the  preparation  is  intrinsically 
more  vigorous.  Engelmann's  experiments  on  the  ureter  show 
that  not  only  excitability,  but  conductivity  also,  appear  to  be 
affected  after  each  contraction,  i.e.  after  a  relatively  short  ex- 
citation, and  only  recover  themselves  during  the  subsequent 
pause,  and  that  the  more  quickly  in  proportion  with  the  original 
excitability  of  the  preparation.  The  "  refractory "  period  of 
contracting  cardiac  muscle  should  also  be  taken  into  considera- 
tion. It  is,  however,  clear  that  if  the  capacity  of  recovery  in 
striated  muscle  is  greater,  and  exceeds  that  of  smooth  muscle,  in 
the  same  proportion  as  its  excitability,  diminution  of  response 
at  the  kathode,  due  to  the  excitatory  process,  may  have 
reached  considerable  proportions  after  the  closure  of  a  strong 
current,  without  any  necessarily  marked  after-effect  on  opening 
the  current,  provided  that  closure  lasts  for  a  few  seconds 
only.  But  it  is  never  possible  to  exclude  a  temporary  effect  upon 
absolute  current-density,  of  such  a  kind  that  with  an  existing 
current  of  a  certain  magnitude,  a  superposed  positive  variation 
will  excite  in  a  lesser  degree  than  before,  independent  of  the 
fatigue  induced  by  the  former.  We  may  therefore  assume,  that 
not  only  the  depression  of  excitability  during  and  after  persist- 
ent polarisation,  but  also  the  depression  of  response  at  the 
kathodic  fibre-points  of  a  muscle  immediately  after  closure  of  a 
strong  current,  depend  essentially  upon  a  local  "condition  of 
fatigue,"  meaning  by  "fatigue"  the  total  changes  in  the  con- 
tractile substance  of  the  muscle,  produced  at  the  seat  of  stimula- 
tion by  the  excitatory  process,  which,  while  they  last,  prevent,  or 
at  least  hinder,  the  rise  of  a  second  excitation.  We  may  there- 
fore conclude  as  the  result  of  all  the  preceding  data,  that  the 
alteration,  positive  or  negative,  of  excitalility  at  the  kathode  of  a 
muscle  traversed  ly  current,  dejxnds  esscnticdly  tqjon  the  state  of 
latent  continuous  excitation,  and  its  consequeiices,  which  vary  ivith 
the  strength  of  the  polarising  current. 


ELECTRICAL  EXCITATION  OF  MUSCLE 


289 


It  is  less  easy  to  formulate  conclusions  as  to  the  manifesta- 
tions of  excitability  at  the  "  physiological  anode "  of  a  muscle, 
during  the  passage  of  current.  The  attempts  at  solving  this 
problem  by  the-  application  of  induction  currents,  opijosed  in 
duration  to  the  polarising  current,  and  traversing  the  whole  intra- 
polar  tract,  have  been  too  ambiguous  to  give  any  decisive  results. 
Von  Bezold,  who  made  the  same  experiments,  though  from  another 
standpoint,  asserts  (10)  that  "both  ascending  and  descending 
galvanic  currents  tlowing  through  the  muscle,  increase  its 
excitability  at  first  to  ascending  make  induction  currents,  so  long 
as  these  do  not  exceed  a  certain  density,  at  and  after  which 
point  the  effect  is  diminutional."  Moreover,  "  the  turning-point  of 
the  curve  of  increase  of  excitability,  in  ratio  with  the  density  of 
the  polarisation  current  as  abscissa,  appears  earlier  when  the 
polarisation  current  is  opposed  to  the  exciting  current,  than  when 
it  is   homodromous   with  it."      When  the  induced  current  is  in 


Fig.  96. 

the  same  direction  as  the  polarising  current,  the  excitation  of 
the  muscle  apparently  ensues  only  because  the  constant  current 
suffers  a  sudden,  evanescent,  positive  variation  at  the  moment 
of  closure  of  the  primary  circuit^  (Fig.  96,  a). 

The  converse  naturally  occurs  when  the  direction  of  the 
exciting  current  is  opposed  to  that  of  the  polarising  galvanic 
current  (Fig.  96,  h). 

It  depends  essentially  upon  the  magnitude  of  variation  in 
intensity  of  the  former,  whether  a  twitch  is  yielded  by  the 
muscle,  or  not.  If  the  line  of  intensity  of  the  (presumably)  very 
weak,  polarising  current  is  represented  by  a  straight  line  above 
the  abscissa,  and  running  parallel  with  it,  it  is  evident  that  while, 
with    uniform    direction    of    excitation    current    and    polarising 

^  Since  the  disappearance  of  induced  currents  does  not  usuallj',  on  account  of  their 
extremely  brief  duration,  give  rise  to  a  break  excitation,  ^\•e  must  not  hesitate  in  the 
cases  cited  to  regard  the  action  of  a  homodromous  induction  current  as  similar  to 
that  of  a  single,  rapidly  disappearing  positive  variation  of  the  galvanic  current. 

U 


290  ELECTRO-PHYSIOLOGY  chap. 

galvanic  current,  the  ascending  portion  only  of  the  superposed 
curve  of  variation  is  concerned  in  the  excitation  of  the  muscle, 
this  is  by  no  means  the  case  when  the  two  interfering  currents 
are  opposite  in  direction.  Here,  under  some  Conditions,  the  de- 
scending as  well  as  the  ascending  portion  of  the  curve  may  have 
an  excitatory  effect  (Griitzner,  cf.  Pfiilgers  Arch,  xxviii.  p.  146)  ; 
in  the  first  case  excitation  would  occur  on  opening,  in  the  second 
on  closing  the  circuit.  With  lower  intensity  of  the  polarising 
galvanic  current,  the  first  effect  would  not,  however,  come  into 
consideration.  But  the  other  would  also  remain  ineffective  if  the 
battery  current  is  so  weak  that  its  closure  iier  se  produces  no 
visible  twitch.  So  long  as  the  deepest  point  of  the  curve  of 
variation  has  not  reached,  or  only  just  reaches,  the  abscissa,  the 
sudden  renewal  of  the  momentarily  weakened,  or  interrupted 
battery  current  will  not  induce  excitation.  It  is  only  when  the 
deepest  point  of  the  curve  of  variation  extends  below  the  line  of 
the  abscissa,  i.e.  when  the  intensity  of  the  exciting  current  is  so 
great  that  it  not  merely  interrupts  the  polarising  constant  cur- 
rent, but  a  certain  fraction  of  it  also  traverses  the  muscle  in  a 
direction  opposed  to  the  constant  current,  that  a  twitch  may 
possibly  follow,  and  to  this  it  must  be  added  that  the  excitatory 
process  will  in  this  case  be  discharged  at  spots  that  were  formerly 
anodic.  Excitation  therefore  occurs  at  the  points  where  the 
constant  current  enters,  not  during  its  jycf-ssage,  but  at  a  minimal 
interval  after  it  has  been  broken.  The  return  of  the  polarising 
current  to  its  original  height,  which  follows  immediately  after, 
will  not  accordingly  produce  excitation,  being  too  low  in  intensity. 
It  is  easy  to  see  that  with  greater  strength  of  the  battery  current, 
the  relations  will  become  yet  more  complicated,  since  both  its 
negative  variation  of  intensity,  and  also  its  recovery  after  previous 
diminution  or  interruption,  may  cause  excitation. 

It  follows  from  the  above  that  the  possibility  of  producing 
any  changes  of  excitability  in  anodic  points  of  the  fibres  by 
means  of  an  induction  current  opposed  in  direction  to  the 
polarising  current,  is  connected  with  very  peculiar  conditions. 

In  the  first  place,  it  appears  to  be  essential  that  the  intensity 
of  the  exciting  current  should  considerably  exceed  that  of  the 
polarising  current,  for  it  is  only  under  these  conditions  that  it  is 
possible  to  conclude  with  any  probability  that,  during  the  closure 
of  the  latter,  that  fraction  of  the  induced  current  remaining  for 


lu  ELECTRICAL  EXCITATION  OF  MUSCLE  291 

excitation  of  the  muscle  is  sufficiently  large  to  provoke  a  twitch, 
where  the  excitability  at  the  anode  has  remained  normal.  If,, 
however,  excitation  was  wanting  in  such  a  case,  we  should  be  fully 
justified  in  concluding  that  there  was  decreased  excitability  at  the 
anodic  fibre  points.  Whether  in  any  given  case  this  theoretical 
assumption  is  sufficiently  justified  is  the  harder  to  determine, 
inasmuch  as  the  exciting  current  differs  essentially  from  the 
polarising  battery  current  in  potential,  as  well  as  in  variation  of 
intensity — a  circumstance  which  is  of  great  significance  to  the 
results  of  excitation.  Brlicke's  investigations  have  made  it  cer- 
tain that  the  excessively  short  duration  of  induced  currents  im- 
plies a  relatively  greater  intensity  in  order  to  excite  a  curarised 
muscle  to  the  same  degree  as  the  galvanic  current  under  similar 
conditions.  Since  it  appears  consistently  that  even  a  very  weak 
battery  current  (2  Dan.  rheochord  res.  =  1—3  cm.)  suffices  to 
inhibit  the  excitatory  action  of  a  heterodromous  induction 
current  discharging  a  maximal  twitch,  so  that  no  effect  can 
be  observed  during  closure  of  the  battery  current  even  when  the 
exciting  current  is  greatly  strengthened,  it  is  surely  legitimate  to 
conclude  that  response  from  the  anodic  points  is  lowered  during 
polarisation. 

Summing  up  what  has  been  said,  it  follows  that  if  a  muscle  is 
continuously  traversed  by  a  galvanic  current,  the  excitability  of 
the  kathodic  points  during  the  passage  is  found  to  be  either 
raised  or  lowered.  The  former  occurs  with  low  intensity  of  the 
polarising  current,  the  latter  with  greater  strength,  or  with  longer 
closure  of  weak  currents.  So  far  as  it  is  possible  to  conclude 
from  electrical  experiments,  the  excitability  of  anodic  points  is 
always  lessened,  or  completely  inhibited,  during  the  passage  of  the 
polarising  current. 

In  the  next  place,  what  occurs  with  regard  to  excitahility  of 
the  poles  on  opening  a  i^olarising  current  ?  These  "  after-effects  " 
may  be  described  shortly.  We  have  already  said  that  after  a 
moderate  closure  of  a  very  weak  electrical  current,  no  after-effect 
can  be  determined  at  the  kathode,  because  the  excitatory  action 
of  single,  homodromous  induction  shocks,  which  is  considerably 
heightened  during  the  polarisation,  resumes  its  original  proportions 
so  soon  as  the  battery  current  is  opened.  If,  on  the  other  hand,  a 
battery  current  of  medium  intensity  is  closed  for  a  long  enough 
period  (1—2  minutes  usually  suffices),  there  is  invariably,  as  in 


292  ELECTRO-PHYSIOLOGY  chap. 

Series  I.  and  II.,  a  diminution  of  excitability  at  the  kathode, 
not  merely  while  the  current  is  passing  but  also  after  the  polaris- 
ing current  has  been  opened.  This  lasts  longer  in  proportion  with 
the  intensity  and  duration  of  the  current.  Such  a  muscle,  after 
prolonged  rest,  possibly  not  for  several  minutes,  will  recover 
itself  so  far  that  an  induction  current  homodromous  with  that 
which  exhibited  twitches  previous  to  polarisation  will  again 
produce  excitation.  Normal  kathodic  excitability  is,  however, 
much  more  quickly  restored,  even  when  spontaneous  recovery  is 
abolished  on  account  of  widespread  local  fatigue,  if  the  polarising 
current  is  reversed  for  a  short  time.  Closely  allied  with  this, 
also,  is  the  fact  that  anodic  excitability  is  usually  considerably 
augmented  after  a  not  too  brief  polarisation  of  a  curarised  muscle, 
provided  the  battery  current  is  of  adequate  intensity. 

Although  these  manifestations  of  the  so-called  ''voltaic 
alternative  "  have  long  been  known,  it  has  not  been  sufficiently 
taken  into  consideration  that  this  is  just  as  much  a  polar,  i.e. 
purely  local,  effect  of  current  as  in  the  excitatory  process  at  the 
kathode.  Heidenhain  (43)  discovered  that  muscles,  the  excita- 
bility of  which  had  been  depressed  by  any  injurious  influences 
{tetanising,  protracted  passage  of  current,  heat,  etc.)  to  such  a 
degree  that  they  did  not  react  perceptibly  even  to  the  closure  of 
very  powerful  currents,  recovered  their  excitability  partially,  at 
least,  after  they  had  been  exposed  for  some  time  to  the  action  of  a 
strong  ascending  or  descending  current,  excitation  occurring  again 
on  opening  the  polarising,  or  closing  a  heterodromous  current,  to 
a  greater  or  less  degree :  Eosenthal  (44)  pointed  out  the  connection 
between  these  facts  and  the  phenomena  of  the  voltaic  alternative 
in  fresh,  non-fatigued  muscle,  which  he  was  the  first  to  investigate. 

According  to  these  observations,  which  are  easy  to  confirm, 
the  response  of  every  muscle  sinks,  with  prolonged  passage  of 
current  in  one  direction,  towards  the  closure  of  such  a  current, 
being,  on  the  contrary,  considerably  augmented  for  the  opening  as 
well  as  closure  of  a  current  in  the  opposite  direction.  The  first 
effect,  as  was  shown  above,  is  dependent  upon  a  state  of  fatigue 
confined  exclusively  to  the  kathodic  points. 

The  experiments  which  led  to  this  conclusion  show,  moreover, 
that  the  increase  in  response  to  closure  of  a  homodromous  current, 
demonstrable  after  break  of  an  adequate  polarising  current,  is 
characteristic  of  the  anodic  points  of  fibres. 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  293 

Since  it  is  a  well-established  fact  that  on  closure  of  current 
excitation  occurs  only  at  the  point  where  it  leaves  the  muscle, 
the  proof  that  excitability  increases  at  the  anode  after  polarisa- 
tion, lies  essentially  in  the  fact  that  the  effects  of  excitation  are 
augmented  with  closure  of  a  polarising  current  in  the  opposite 
direction.  It  is  conceivable  that  such  changes  in  excitability 
might  extend  over  a  larger  or  smaller  part  of  the  tract  of  muscle 
traversed,  although  the  complete  failure  of  electrotonic  alterations 
of  excitability  in  the  intrapolar  tract  during  the  passage  of  the 
current  renders  it  a  ^priori  very  improbable.  Direct  electrical  exci- 
tation of  different  points  in  the  continuity  of  a  previously  polarised 
muscle,  moreover,  affords  direct  proof  that  just  as  little  as  the 
negative  after-effect  of  polarisation  extends  beyond  the  physio- 
logical kathode,  does  the  positive  after-effect  pass  beyond  the 
limits  of  the  physiological  anode,  provided  only  that  the  polarising 
current  is  not  too  powerful,  otherwise  a  complex  of  disturbances 
might  arise  through  the  formation  of  secondary  electrodes. 

Undoubtedly  the  alterations  of  excitability  in  question  during, 
and  after,  the  passage  of  current  through  a  muscle,  stand  in  very 
close  relation  with  the  effects  of  excitation  and  inhibition  already 
described,  being  indeed  only  another  aspect  of  the  same  facts. 
We  have  seen  that  when  the  electrical  current  acts  as  a 
continuous  excitation  at  the  kathode,  the  alterations  of  excita- 
bility, or  capacity  of  response  observed  are  its  necessary  conse- 
quences, and  equally  under  all  conditions  must  we  predicate 
depression  of  excitability  at  the  anode  whenever  an  existing 
excitation  is  inhibited  during  closure.  The  complete  reversal 
at  break  of  the  polarising  current  follows  as  cogently  from  the 
reversal  of  polar  manifestations  of  excitation  and  inhibition. 
Since  neither  excitatory  nor  inhibitory  phenomena  are  produced 
by  the  direct  action  of  current  within  the  intrapolar  area,  but  only 
appear  as  changes  induced  at  the  poles,  or  by  the  effectuation  of 
secondary  electrodes,  it  is  a  iiriori  certain  that  there  can  be  no 
question  of  alteration  of  excitability  within  the  intrapolar  tract  by 
direct  action  of  current  in  v.  Bezold's  sense — nor,  as  we  shall  see, 
does  any  such  alteration  exist. 

Nor  is  there  legitimate  ground  for  assuming  changes  of 
conductivity  within  the  intrapolar  tract,  and  the  experiments  of 
V.  Bezold  in  this  direction  can  hardly  be  regarded  as  convinc- 
ing.     He  investigated  the  effect  of  polarising  a  tract  of  muscle 


294  ELECTRO-PHYSIOLOGY 


3  mm.  long,  upon  the  conduction  of  a  wave  of  excitation  set  up 
beyond  its  limits.  He  found  that  the  conductivity  of  the 
polarised  section  of  the  muscle  diminished  in  proportion  with 
the  strength  of  current  and  length  of  its  passage.  At  a  given 
degree  of  polarisation,  the  power  of  conducting  seemed  to  be 
completely  abolished.  (This,  e.g.,  was  the  case  after  the  current 
from  4  Dan.,  with  a  rheochord  resistance  of  100,  had  been  sent 
through  a  tract  of  muscle  3  mm.  long,  for  40  sees.)  Von  Bezold 
affirms  that  the  substance  of  muscle,  like  that  of  nerve,  is 
"  paralysed "  by  the  current.  This  paralysis  he  describes  as  a 
defect,  or  inhibition,  of  conductivity,  although  the  apparent  injury 
to  the  muscular  tract  does  not  prevent  it  from  being  thrown  into  a 
state  of  local  excitability  by  external  stimuli  as  rapidly  as  before. 
Von  Bezold  did  not  inquire  into  the  reaction  of  different  sections 
of  the  intrapolar  tract  with  reference  to  changes  in  conductivity, 
but  he  inclines  to  the  view  "  that  the  curve  of  defect  in  the  intra- 
polar tract,  as  in  the  parallel  case  of  nerve,  sinks  from  either  pole 
towards  the  middle." 

It  is  the  more  advisable  in  this  connection  to  investigate 
Engelmann's  experiments  on  the  effect  of  polarisation  upon  the 
conductivity  of  smooth  muscle,  because  while  there  are  manifold 
analogies  between  the  smooth  muscle  of  the  ureter  and  striated 
muscle,  as  regards  response  to  the  electrical  current,  there 
appear  in  this  instance  to  be  essential  differences  between  the 
data  obtained  by  the  author  from  striated  muscle,  and  Engel- 
mann's observations  on  the  ureter. 

He  finds  that  conductivity  in  a  polarised  tract  of  ureter 
diminishes  in  the  side  towards  the  anode,  and  increases  in  that 
towards  the  kathode.  The  magnitude  of  the  changes  is  maximal 
at  the  poles.  The  length  of  the  area  of  depression  increases 
with  strength  and  intensity  of  current,  conduction  being  finally 
abolished  in  the  whole  intrapolar  tract.  When  the  wave  of 
contraction  started  from  a  point  above  an  ascending  polarised 
section  of  the  ureter,  Engelmann  observed  that  it  traversed  the 
entire  intrapolar  tract — if  the  polarising  current  was  very  weak — 
though  with  a  marked  diminution  at  the  anode.  With  strong 
currents  the  wave  disappeared  altogether  at  this  point,  and  with 
still  stronger  (persistent  contraction  at  the  kathode),  it  died  out 
even  at  the  kathode. 

With  regard,  firstly,  to  v.  Bezold's  experiments,  they  by  no 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  295 

means  prove  that  the  conductivity  of  the  ivliole  intra2Jolar  tract 
is  diminished  or  abolished,  it  being  indeed  much  too  short.  The 
inhibition  of  the  wave  of  contraction  might  equally  have  its 
seat  at  the  anode,  if,  as  certainly  appears  from  Engelmann's 
experiments  on  the  ureter,  it  is  true  that  the  conductivity  of  the 
muscular  substance  is  considerably  depressed  there  as  well  as  at 
the  kathode,  since  at  the  strength  of  the  polarising  current 
employed  a  persistent  contraction  must  in  any  case  be  present, 
and  since,  as  we  may  legitimately  conclude  from  Engelmann's 
observations,  a  contracted  point  may.  Under  certain  conditions, 
interrupt  the  conductivity  of  excitation. 

The  next  point,  therefore,  was  to  test  the  conductivity  of  the 
muscle-substance  at  the  anode  as  well  as  at  the  kathode,  and  to 
ascertain  its  dependence  on  the  strength  and  duration  of  the 
current.  For  this  purpose  a  strongly  curarised  sartorius  muscle  was 
connected  in  the  usual  manner  with  the  unpolarisable  electrodes 
of  Hering's  double  myograph,  the  centre  of  the  muscle  being  fixed 
with  oil-clay,  and  the  changes  of  form  of  both  halves  recording 
themselves  on  a  smoked  surface.  As  a  rule,  the  lower  end  of 
the  sartorius  was  excited  with  single  descending  make  induction 
shocks.  The  exciting  current  escaped  by  one  electrode  of  the 
double  myograph ;  its  entry  was  arranged  by  a  loop  of  thread, 
moistened  with  0'5  %  salt  solution,  and  inserted  into  the 
clay  tip  of  an  ordinary  unpolarisable  electrode,  in  order  to 
obstruct  the  changes  of  form  in  either  half  of  the  muscle  as  little 
as  possible  during  excitation.  In  the  immediate  vicinity  of  the 
fixed  part,  corresponding  roughly  with  the  centre  of  the  muscle,  an 
electrode  of  the  same  kind  enabled  the  polarising  battery  current 
to  leave  or  enter  the  muscle,  the  whole  upper  part  of  which  was 
traversed.  A  wave  of  contraction  discharged  at  the  lower  end 
of  the  sartorius  traverses  the  fixed  part  without  interruption, 
and  both  halves  of  the  muscle  shorten,  as  a  rule,  approximately 
so  long  as  the  polarising  circuit  remains  open.  Even  a  weak 
galvanic  current  (ascending  or  descending)  passing  through  the 
upper  half  of  the  muscle  continuously,  exerts  no  perceptible 
influence  on  the  size  of  twitch  in  either  half.  When,  however, 
the  intensity  of  the  polarising  current  is  raised  (to  about  2  Dan. 
=  100  E.),  the  kathode  being  in  the  centre  of  the  muscle,  a  pro- 
nounced inhibition,  in  proportion  with  the  strength  and  direction 
of  the  current,  in  every  case  interferes  with  the  propagation  of  the 


296  ELECTRO-PHYSIOLOGY 


wave  of  contraction  initiated  in  the  non-polarised  section  of  the 
muscle.  In  the  first  place,  it  is  seen  that  the  two  halves  of 
the  muscle  do  not,  as  before,  contract  equally,  inasmuch  as  the 
curves  of  twitch  in  the  polarised  half  become  smaller  and  smaller 
during  the  passage  of  current,  while  on  the  directly-excited  half 
they  remain  unaltered.  Finally,  with  renewed  excitation  of  the 
non-polarised  half  of  the  muscle,  changes  of  form  on  the  farther 
side  of  the  fixed  spot  fail  altogether ;  the  wave  of  contraction  is 
unable  to  get  past  the  kathode. 

According  to  v.  Bezold  we  should  expect  that  the  whole 
intrapolar  tract  would  by  this  time  have  become  incapable  of 
conduction.  This,  however,  is  emphatically  contradicted  by  the 
circumstance  that  when  the  polarising  current  enters  at  the  middle 
of  the  muscle,  i.e.  when  the  anode  is  at  that  part,  there  is  never, 
even  on  applying  very  strong  galvanic  currents,  and  prolonging  the 
passage  of  current  indefinitely,  any  perceptible  impediment  to 
the  propagation  of  a  wave  of  contraction ;  sometimes,  as  we  shall 
see,  the  direct  contrary.  There  can  therefore  be  no  doubt  that 
fibre-points  which  have  served  for  some  time  as  the  exit  of  a 
sufficiently  strong  electrical  current,  fall  into  a  condition  in 
which  they  become  incapable  of  propagating  a  wave  of  excitation 
from  one  side  to  the  other  of  the  section.  This  impenetrability 
of  the  kathode  has  also  been  established  for  nerve  by  Hermann 
and  Werigo  (infra).  The  conditions  of  its  development  are  pre- 
cisely similar  to  those  of  muscle. 

That  it  is  not  the  persistent  closure  contraction,  localised  at 
the  kathode  as  such,  which  interferes  with  propagation,  is  seen 
(apart  from  the  fact  that  both  halves  of  the  muscle  frequently 
contract  equally,  although  at  the  kathode,  in  the  centre  of  the 
muscle,  there  is  also  a  marked  continuous  contraction),  in  that 
the  inhibition  is  most  pronounced  when  a  persistent  descending 
current  in  the  upper  half  of  the  muscle  has  reduced  the  original 
persistent  closure  contraction  to  a  minimum.  It  is  therefore 
legitimate  to  assume  that  the  local  fatigue  of  muscle-substance 
produced  by  current  at  the  kathode  is  the  fundamental  cause  of 
the  inhibition  of  conductivity  in  that  region.  With  regard  to 
the  above  observations  on  the  rapid  decrease  of  response  at 
kathodic  points  during  polarisation,  it  might  appear  strange  that 
with  the  given  experimental  conditions  the  inhibition  of  con- 
ductivity at  the  kathode  is   first  exhibited  at  a  comparatively 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  297 

late  period  after  the  closure  of  fairly  strong  currents.  The  cause 
of  this  deviation  is  presumably  to  be  sought  in  the  different 
mode  of  exit  of  the  current  in  either  case.  For  while  in 
the  first  case  this  occurs  at  the  ends  of  the  fibres,  in  the 
other  the  "  physiological  kathode "  lies  at  the  centre  of  the 
muscle,  where  current  density  must  be  less  on  account  of  the 
larger  section  ;  while,  on  the  other  hand,  the  oblique  course  of  the 
isolated  lines  of  current  directed  towards  a  small  zone  of  the 
muscle  surface  causes  the  innermost  fibres  to  be  less  strongly 
excited  than  those  at  the  periphery,  since  the  current  leaves  the 
former  with  a  less  density  than  the  latter.  Accordingly  we 
always  find  that  when  the  exit  of  the  current  occurs,  as  described 
above,  at  the  centre  of  the  muscle,  much  stronger  currents 
will,  as  a  rule,  be  rec^uired  to  produce  a  make  twitch  than 
under  the  opposite  conditions.  So  long  as  the  total  section  of 
the  muscle  at  the  exit  of  the  current  is  not  fatigued  by  pro- 
longed passage  of  current,  each  wave  of  excitation  arriving  at  the 
kathodic  section  will  endeavour  to  pass  beyond  it,  since  it  can — 
so  to  speak — glide  under  the  most  strongly  excited  peripheral 
zone,  and  is  first  completely  inhibited  when  the  muscle  is,  if  we 
may  so  express  it,  functionally  separated,  i.e.  divided  by  a  small 
unexcitable  zone  into  two  excitable  sections,  from  the  continuance 
of  the  state  of  local  excitation.  This  separation  makes  it  con- 
ceivable that,  as  a  rule,  tolerably  protracted  polarisation  by 
fairly  strong  currents  is  required  in  order  to  depress  conductivity 
at  any  point  in  the  continuity  of  the  muscle  to  such  a  degree 
that  an  approaching  wave  of  excitation  will  be  hindered  in  its 
progress.  If  the  upper  half  of  the  muscle,  as  we  have  been 
assuming,  is  polarised  in  a  descending  direction,  and  the  current 
then  suddenly  reversed,  the  vigorous  make  excitation  discharged 
at  the  previously  anodic  end  of  the  muscle,  fails  to  pass  beyond 
the  section  which  has  been  rendered  incapable  of  conducting  by 
the  sustained  excitation  at  the  kathode,  and  at  closure  only  the 
directly  excited  and  formerly  polarised  half  of  the  muscle  will 
twitch,  while  the  other  half  beyond  the  fixed  part  remains 
passive. 

Conductivity  is  recovered,  under  certain  conditions,  when  the 
current  is  broken  ;  but  if  it  has  been  too  strong,  or  if  polarisation 
is  prolonged  unduly,  the  kathodic  section  may  remain  per- 
manently incapable  of  conducting. 


298  ELECTRO-PHYSIOLOGY 


We  have  seen  that,  contrary  to  the  behaviour  of  the  ureter 
as  observed  by  Engelmann,  the  conductivity  of  striated  muscle 
(sartorius)  exhibits  no  perceptible  diminution  under  the  influence 
of  the  anode.  This  is  the  more  striking  since  there  is  complete 
agreement  in  both  cases  as  regards  direct  excitability.  And  it  is 
further  less  likely  that  there  should  be  any  fundamental  diverg- 
ence between  the  two  cases,  since  anodic  inhibition  of  conduct- 
ivity is  very  pronounced  in  nerve  also.  The  difference  must  be 
due  simply  to  external  factors,  among  which  may  be  instanced  the 
thickness  of  muscle  and  transverse  course  of  the  lines  of  current. 
The  fact  above  alluded  to,  that  kathodic  inexcitable  points  may 
be  so  modified  by  the  influence  of  the  anode  as  to  become  capable 
of  excitation  once  more  as  soon  as  the  electrical  current  leaves 
the  muscle  at  the  points  in  question,  only  show  that  they  have 
a^ain  become  sensitive  to  direct  electrical  excitation.  But  since 
we  may  conclude  from  this  that  alterations  of  muscular  excit- 
ability by  no  means  invariably  entail  corresponding  alterations  of 
conductivity,  it  is  conceivable  that,  notwithstanding  the  restora- 
tion of  direct  excitability,  the  power  of  conduction,  i.e.  of  being 
thrown  into  excitation  indirectly  by  a  wave  of  contraction  from 
some  other  point,  may  sometimes  be  permanently  abolished  at  the 
kathode.  Experiments  with  passage  of  current  through  one  half 
of  a  curarised  sartorius  indicate,  however,  an  opposite  result,  i.e. 
even  in  cases  where  polarisation  has  been  so  long  continued  that 
there  can  be  no  question  of  spontaneous  restoration  of  the  now 
incapable  muscle  section,  the  power  of  propagating  the  excitatory 
process  has  been  invariably  and  even  permanently  restored  under 
the  influence  of  the  anode,  provided  the  current  used  be  suffi- 
ciently powerful. 

In  this  way  it  lies  in  our  power  to  render  any  given  section 
of  a  muscle  with  parallel  fibres  permeable  or  impermeable  to  a 
wave  of  contraction  from  without,  according  as  we  make  the 
current  traversing  one  half  of  the  muscle  enter,  or  pass  out,  at  the 
centre  of  the  muscle. 

As  regards  alterations  of  excitability  in  a  polarised  muscle, 
we  have  direct  proof  that  whether  extra-  or  intrapolar  they  do 
not  extend  beyond  the  physiological  kathode  or  anode,  and  there 
is  no  reason  to  infer  the  opposite  for  alterations  of  conductivity. 
All  the  evidence,  on  the  contrary,  goes  to  show  that  the  one  as  well 
as  the  other  must  be  regarded  strictly  as  a  polar  effect  of  current. 


ELECTRICAL  EXCITATION  OF  MUSCLE  299 


The  Electkical  Excitation  of  Unfibrillated  Protoplasm 

The  action  of  the  electrical  current  upon  muscle  has  long- 
since  attracted  the  attention  of  physiologists  ;  the  consequences 
of  the  passage  of  current  through  unfibrillated  protoplasm  (which 
are  of  the  greatest  interest  in  a  theoretical  connection)  have  until 
lately  been  almost  entirely  disregarded,  and  only  a  few  isolated 
observations  indicate  that  we  are  here  concerned  with  facts  of 
wide-reaching  significance. 

In  connection  with  certain  theoretical  views  as  to  the  causa- 
tion of  plasmatic  movements — of  the  streaming  movements  in 
vegetable  cells  in  particular — Bequerel  examined  the  effect  of  a 
strong  current  flowing  through  a  spiral  wire  round  a  decorticated 
cell  of  Chara.  No  effect  was  produced,  whether  the  axis  of  the 
wire-coil  was  parallel,  or  at  right  angles,  to  the  axis  of  the  cell. 
Later  experiments  were  equally  negative ;  no  action  at  a  distance 
of  the  current  upon  any  sort  of  excitable  protoplasm  could  be 
detected,  so  that  it  may  be  taken  as  certain  that  such  an  action, 
generally  speaking,  does  not  exist. 

In  consequence  of  the  direct  action  of  weak  induction 
currents,  Klihne  and  Engelmann  observed  the  movement  of 
Amoebse  to  ho.  at  first  arrested  and  then  resumed  after  a  short 
time.  With  stronger  induction  shocks  the  Amcebce  assumed  a 
globular  shape  by  the  withdrawal  of  all  their  pseudopodia,  which 
at  once  arrested  all  molecular  movement.  Finally,  with  very 
strong  excitation  the  sphere  of  protoplasm  may  collapse  and 
extrude  its  endoplasm,  which  is  equivalent  to  the  total  destruction 
of  the  animal  (45). 

Ehizopods  with  numerous  long  and  slender  pseudopodia  with- 
draw these  when  electrically  excited,  and  in  this  case  it  is  especi- 
ally remarkable  that  those  j^seuclopoclia  which  lie  at  right  angles  to  the 
lines  of  current  shoiv  no  change,  or  at  any  rate  change  only  ivith  far 
stronger  currents  than  those  vjhich  lie  jiarcdlel  to  it,  a  fact  which 
calls  to  mind  the  similar  behaviour  of  muscle  under  similar  con- 
ditions. Klihne  (46),  when  tetanising  Actinosphcerium  with  the 
alternating  currents  of  an  induction  coil,  observed  that  the 
pseudopodia  lying  along  the  line  hetioeen  the  tioo  electrodes  soon  became 
varicose  ;  the  granular  protoplasm  along  the  axial  ray  gathered 
itself  into  little  spheres  and  spindles,  which  flowed  towards  the 


300 


ELECTRO-PHYSIOLOGY 


body,  while  the  entire  pseudopocl  was  gradually  withdrawn. 
Since  we  shall  frequently  have  occasion  to  refer  to  these  rhizo- 
pods  (which  are  exceptionally  well  adapted  to  electrical  excita- 
tion experiments)  it  is  advisable  here  to  introduce  some  further 
remarks  as  to  their  structure.  The  fairly  large  globular  body  of 
Actinosphserium  exhibits  two  distinct  layers — a  darker,  central, 
richly  nucleated  mass  (endoplasm),  and  a  lighter,  vacuolated, 
cortical  layer  (Fig.  97).  Each  vacuole  is  filled  with  fluid, 
bounded  by  a  wall  of  homogeneous,  finely  granular  protoplasm  : 


Fig.  Q7.—Actinosphcerium  eichorne.    Polar  effects  of  excitation  with  passage  of  a  constant 
electrical  current.    (Verworn.) 


this  same  protoplasm  forms  part  of  the  bristle-shaped  pseudopodia 
which  stand  out  from  the  body  in  all  directions,  and  exhibit  a 
characteristic  differentiation  of  structure — an  "  axial  ray  "  of  firmer 
consistence  covered  by  the  somewhat  fluid  protoplasm  like  a  rind. 
The  contraction  phenomena  described  by  Kiihne  manifest  them- 
selves in  a  constant  manner  to  a  given  mode  of  excitation.  "  In 
consequence  of  stimulation  the  axial  ray  of  a  pseudopod  in  the  un- 
excited  state  of  almost  homogeneous  enveloping  protoplasm,  gathers 
itself  together,  while  streaming  towards  the  body  upon  the  axial  ray, 
in  small,  solitary,  fusiform  or  globular  varicosities,  between  which 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  ;j01 

the  axial  ray  lies  completely  bared  at  many  points.  The  spindles 
and  spheres  glide  slowly  upon  the  axial  ray  (which  at  the  same 
time  is  being  withdrawn  into  the  body),  in  a  centripetal  direction, 
sometimes  coalescing,  and  finally  flowing  entirely  into  the  proto- 
plasm of  the  cortical  layer."  If  the  excitation  is  strengthened, 
or  prolonged  continuously,  the  fluid  vacuoles  of  the  cortical  layer 
begin  to  collapse,  after  the  pseudopodia  have  been  withdrawn 
from  the  excited  spot  (or  may  be  from  the  entire  body),  because  the 
protoplasm  which  forms  their  walls  shrinks  more  and  more  inwards. 
This  gives  to  the  body  an  irregularly-bounded,  lumpy  surface. 
Finally,  with  still  stronger  excitation,  the  protoplasm  begins  to 
disintegrate  into  granules,  by  a  gradual  process  beginning  at  the 
surface,  and  progressing  slowly  inwards  until  the  central  mass  is 
involved,  when — unless  the  excitation  is  stopped — the  entire  body 
is  destroyed.  Short  of  such  total  disintegration  it  is  possible  for 
the  undestroyed  remainder  to  reconstitute  itself  into  a  perfect, 
though  correspondingly  diminished  Actinosphaerium  (Verworn, 
47).  With  sufflciently  strong  excitation  the  plasmatic  bands 
and  threads  of  certain  vegetable  cells  {Tradescantia)  will  comport 
themselves  like  the  pseudopodia  of  rhizopods.  With  weaker  ex- 
citation there  may  frequently  be  observed,  as  in  the  case  of 
independent  amoeboid  protoplasm,  a  slowing  and  arrest  of  the 
spontaneous  streaming  movements,  followed  by  the  formation  of 
varicosities,  lumps,  and  so  forth,  upon  strengthening  the  excitation. 
Kiihne  observed  that  these  effects  were  localised  to  a  restricted 
portion  in  correspondence  with  localised  excitation.  If  a  large 
cell  of  Tradescantia  is  arranged  transversely  to  a  pair  of  fine- 
pointed  electrodes  lying  close  together,  it  is  possible  to  send 
currents  of  great  density  through  a  limited  part  of  the  cell. 
With  gradual  approximation  of  the  secondary  to  the  primary 
coil  the  movements  of  only  a  portion  of  the  cell  are  arrested,  and 
a  formation  of  swellings,  lumps,  and  knots  ensues,  which  may  be 
subsequently  reinvolved  in  the  stream  of  the  intact  protoplasm. 
The  circulating  plasma  of  Vallisneria,  Chara,  Mtella,  etc.,  when 
submitted  to  electrical  excitation,  always  exhibits  a  retardation 
and  subsequent  arrest  of  the  streaming  movements. 

The  phenomena  exhibited  by  certain  kinds  of  protoplasm, 
when  submitted  to  the  action  of  the  constant  current,  are  of  far 
greater  interest.  The  first  observations  in  this  direction  are  due 
to  Kiihne,  who,  as  long  ago  as  1864,  drew  attention  to   the  re- 


302  ELECTRO-PHYSIOLOGY 


markable  and  in  many  respects  important  reactions  of  Actino- 
sphserium  to  the  galvanic  current.  We  shall  in  the  main  follow 
the  account  given  by  Verworn  (I.e.)  who  has  recently  repeated 
these  observations,  completing  and  extending  them  in  various 
directions.  In  regard  to  method  it  should  be  observed  that  un- 
polarisable  electrodes  were  exclusively  employed  in  these  experi- 
ments. The  Actinosphserium  is  placed  in  a  few  drops  of  water 
in  a  little  excitation  chamber,  made  by  cementing  two  slabs  of 
porous  clay,  joined  by  two  transverse  partitions  of  cement,  on  to 
a  large  object  glass,  so  as  to  form  a  (closed)  rectangular  space,  to 
the  clay  sides  of  which  brush  electrodes  were  applied,  so  that 
current  could  traverse  the  chamber  in  approximately  parallel 
lines.  In  consequence  of  the  high  resistance  in  the  circuit,  com- 
paratively high  electromotive  force  must  be  used  in  order  to 
obtain  distinct  effects,  which,  however,  in  such  cases  are  perfectly 
characteristic.  At  closure  of  the  current,  in  the  first  place,  the 
pseudopodia,  both  on  the  anodic  and  kathodic  side  of  the  globular 
body,  become  varicose,  and  begin  to  contract  as  described  above  ; 
whereas  the  ]3seudopocls  that  are  situated  at  right  angles  to  the  line 
of  current  exhibit  no  changes.  On  the  kathodic  side  the  effects  of 
excitation  are  comparatively  inconsiderable  and  very  evanescent ; 
the  pseudopodia  soon  resume  their  normal  aspect.  The  corre- 
sponding effects  on  the  anodic  side,  on  the  contrary,  proceed  unin- 
terrvptedly  as  long  as  the  current  is  jj^ssing.  Little  by  little  the 
pseudopodia  are  completely  withdrawn  ;  the  vacuoles  in  the 
cortical  layer  begin  to  collapse  and  empty  themselves  of  fluid ; 
a  gradual  dissolution  of  the  body -mass  takes  place  on  the 
anodic  side,  while  the  protoplasm  disintegrates  into  granules.  In 
this  manner  a  concave  gap  is  gradually  formed  on  the  anodic  side, 
while  a  very  slow  retractation  of  pseudopods  is  taking  place  over 
all  the  rest  of  the  body.  Finally,  the  Actinosphasrium  becomes 
sickle-shaped  like  a  new  moon,  the  greater  part  of  the  body-mass 
having  undergone  disintegration  into  granules  (Fig.  97). 

If  the  circuit  is  opened  at  a  moment  when  the  pseudopodia  are 
still  in  a  normal  state,  except  on  the  anodic  side,  the  corrosion  at 
the  anode  ceases  directly,  and  the  pseudopods  on  the  kathodic 
side  become  varicose  in  about  the  same  degree  as  had  taken  place 
immediately  after  the  closure  of  the  circuit.  This  effect  is,  how- 
ever, very  evanescent ;  the  pseudopods  soon  recover  their  normal 
aspect,  while  the  anodic  gap  gradually  fills  up  at  the  same  time, 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  303 

and  a  complete  individual  is  formed  again,  although  on  a  smaller 
scale.  With  weaker  currents  the  process  generally  stops  short  of 
the  collapse  of  vacuoles,  only  the  gradual  retraction  of  pseudopodia 
on  the  anodic  side  is  produced  ;  and  there  is  no  sign  of  any 
kathodic  break  eftect.  The  rapidity  with  which  all  the  above- 
described  phenomena  develop  is  greater  with  increased  strength 
of  current.  At  closure  of  very  strong  currents  the  granular  dis- 
integration on  the  anodic  side  begins  almost  instantly,  and  then 
progresses  more  and  more  gradually  towards  the  centre  as  long  as 
the  current  is  passing. 

According  to  Verworn  the  slow  retraction  of  pseudopods  on  the 
general  body-surface  that  takes  place  during  a  prolonged  passage 
of  current  is  to  be  regarded  as  a  secondary  process,  arising  from 
the  disintegration  that  has  just  taken  place  at  the  anode,  and 
stimulates  the  protoplasm,  inasmuch  as  it  always  commences  after 
a  considerable  loss  of  substance  has  become  apparent. 

From  the  above-described  changes  we  may  easily  predict  the 
consequences  of  alternating  currents.  With  moderately  frequent 
stimuli  the  pseudopodia  at  both  poles  begin  to  exhibit  varicosities, 
and  also  with  stronger  currents  the  granular  break-down  proceeds 
po^ri  'passu  from  both  sides.  It  is  worthy  of  note  that  with  very 
rapid  reversal  of  current,  effects  that  are  in  progress  hccome  arrested, 
to  recommence  ivith  the  adoption  of  a  slovxr  rhythm. 

Verworn  pointed  out  that  Polystomella  crispa  —  a  marine 
Foraminifer  with  numerous  very  fine  pseudopodia,  forming  a  com- 
plex and  retiform  anastomosis,  upon  which  the  phenomena  of 
"  granular  currents  "  described  by  Max  Schultze  are  well  exhibited 
— -reacts  in  precisely  the  same  way  to  the  constant  current.  "  At 
make  of  a  current  all  the  granules  in  the  pseudopodia  of  the  anodic 
side  begin  to  flow  in  a  centripetal  direction,  and  at  the  same  time 
are  slowly  retracted,  and  the  longer  the  excitation  continues  so 
much  the  fewer  and  shorter  are  the  pseudopodia  which  protrude 
from  the  cortex,  until  before  long  there  is  a  total  disappearance 
of  pseudopods  on  the  anodic  side."  On  the  kathodic  side  no  such 
change  is  visible,  the  streaming  of  granules  goes  on  as  usual,  and 
the  pseudopodia  remain  extended  ; — "  they  may  even  lengthen  con- 
siderably, or  make  their  appearance  at  closure  of  the  current  at  a 
kathodic  area  previously  free  of  pseudopods,  the  flow  of  granules 
being  now  in  a  centrifugal  direction."  In  this  case,  as  before, 
no  change  could  be  observed  at  or  after  closure  of  the  circuit  in 


304  ELECTRO-PHYSIGLOGY 


such  pseudopodia  as  lay  across  the  lines  of  current.  Verworn 
was  unable  to  detect  any  definite  kathodic  break  effect. 

The  excitation  changes  that  are  observable  under  similar 
conditions  in  Pelomyxa  palustris  are  of  no  less  interest.  Pelomyxa 
is  a  solid  mass  of  naked  protoplasm,  often  as  much  as  2  mm.  in 
size,  which  is  rendered  very  opaque  by  the  large  quantity  of  sand 
and  mud  englobed  by  the  animal.  The  movements  are  extremely 
sluggish,  and,  as  in  many  Amceba?,  consist  in  a  flow  of  the  endo- 
plasm  along  the  body-axis  in  a  given  direction,  with  a  bending 
round  and  backward  flow  along  both  sides.  In  this  way  a  blunt 
process  in  the  direction  of  the  axial  current  is  formed,  at  tlie 
margin  of  which  a  hyaline  border  is  often  distinguishable.  Ex- 
citation produces  a  variety  of  effects  according  as  it  involves  the 
entire  surface,  or  is  localised  to  one  spot,  and  is  strong  or  weak. 
"  Weak  prolonged  stimuli  acting  upon  the  whole  body,  e.g.  vibra- 
tions, produce  a  very  gradual  but  complete  balling  of  the  body. 
Weak  localised  stimuli  produce  a  gradual  withdrawal  of  the  ex- 
cited part.  Strong  stimuli  {e.g.  by  chemical  reagents)  acting 
upon  the  body  likewise  produce  a  spherical  rounding,  while  at 
the  same  time  there  is  an  escape  of  the  granular  endoplasm, 
in  consequence  of  the  disintegration  of  the  outer  protoplasmic  coat 
— this  escape  is  partial  with  localised  excitation.  The  granulated, 
disintegrating  protoplasm  bursts  out,  and  the  appearance  is  the 
same  as  when  Actinosphterium  is  submitted  to  the  action  of  strong- 
currents."  A  sulflciently  strong  galvanic  current  acts  upon  Pelo- 
myxa with  the  same  results  (Fig.  98). 

At  closure  the  contents  of  the  body  burst  forth  on  the 
anodic  side,  and  as  in  Actinosphsrium,  the  disintegration  spreads 
more  and  more  in  the  direction  of  the  kathode,  until  the  last 
trace  of  protoplasm  has  disappeared.  This  process  of  disintegra- 
tion passes  with  diminishing  rapidity  from  the  anode  to  the 
kathode  in  about  -g-  to  I-  minute,  with  currents  of  equal  efficacy, 
at  the  end  of  which  period  the  individual  is  completely  abolished. 
At  first  the  process  is  extremely  sudden,  then  slower,  until  it 
gradually  becomes  imperceptible.  It  passes  over  the  whole  body 
in  the  form  of  an  annular  constriction,  starting  from  the  anode 
and  advancing  towards  the  kathode ;  that  portion  of  the  body- 
mass  which  is  on  the  anodic  side  of  the  constriction,  i.e.  which 
has  been  traversed  by  it,  is  in  a  state  of  granular  disintegration ; 
that  portion  which   is   on  the  kathodic  side  is  still  normal  and 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  305 

living.  "  If  the  current  is  hroJcen  when  the  process  of  destruction 
has  involved  only  a  small  portion  of  the  entire  mass,  the  disinte- 
gration ceases  to  progress,  whilst  a  swelling  of  granular  disinte- 
grated protoplasm  suddenly  breaks  out  at  the  kathode,  similar  to 
that  which  appeared  at  the  anode  at  the  closure  of  the  circuit. 
But  this  process  at  the  kathode  makes  no  further  progress  after 
the  opening  of  the  circuit."  The  smallest  undestroyed  portion  of 
protoplasm  is  sufficient  to  form  a  new  individual  on  a  smaller 
scale.  With  weaker  currents  the  anodic  effects  may  be  preceded 
by  a  long,  latent  period  (1  minute  or  more).  On  Pelomyxa, 
according  to  Yerworn,  the  action  of  induced  currents,  and  of  con- 


hc:^?^::^' 


^^Qs^^^^s^i.  . 


Fig.  'dS,.— Pelomyxa  palustris.    Polar  excitation  effects  witli  jjassage  of  a  constant  current. 

(Verworn.) 

stant  currents  of  brief  duration,  is  particularly  striking ;  at  a 
given  current  strength  only  a  kathodic  break  excitation  is  obtained, 
whereas  with  currents  of  longer  duration  an  ctnoclic  make  excita- 
tion makes  its  appearance.  The  effects  are  thus  contrary  to 
those  obtained  on  muscle,  not  only  as  regards  the  law  of  polar 
excitation,  but  also  as  regards  the  manner  in  which  make  and 
break  excitation  depend  upon  the  duration  of  the  exciting  current. 
Various  forms  of  Amoeba,  investigated  by  Verworn  {A.  Umax, 
verrucosa,  and  cliffluens),  exhibited  some  apparently  considerable 
divergences  from  the  phenomena  observed  on  Pelomyxa :  at  any 
rate  with  the  strength  of  current  made  use  of,  instead  of  the 
destruction  of  the  anodic  pole  of  the  body,  a  protrusion  (forma- 
tion of  pseudopodia)  was  produced  at  the  kathodic  pole.     At  make 

X 


306  ELECTRO-PHYSIOLOGY 


of  the  constant  current  the  first  effect  is  usually  a  momentary 
arrest  of  the  flow  of  granules,  followed  by  the  sudden  protrusion 
of  a  hyaline  pseudopod  from  the  anterior  end  of  the  body, 
directed  in  a  straight  line  towards  the  kathode.  In  the  case  of 
Amoeba  limax  this  powerful  pseudopod  extends  to  a  considerable 
length,  and  draws  the  entire  body-mass  into  itself,  so  that  the 
amceba  following  the  direction  of  current  creeps  towards  the 
kathode  by  degrees,  in  its  normal  form.  If  the  current  is 
suddenly  reversed  during  this  period,  the  flow  of  granules  and  the 
progress  of  the  amoeba  are  reversed  in  direction — with  a  strong 
current— and  it  is  possible  by  frequent  alternation  to  obtain  con- 
tinuous movements  of  the  amoeba  in  opposite  directions.  It  is 
easy  to  show  that  the  action  in  this  case  is  essentially  similar  to 
that  witnessed  in  Actinosphserium,  Polystomella,  and  Pelomyxa, 
although  obvious  signs  of  excitation  cannot  be  detected.  If,  as  can 
hardly  be  disputed,  we  may  reckon  as  eflects  of  excitation  the  forma- 
tion of  varicosities  in  the  pseudopods,  along  with  their  retraction, 
and  the  eventual  partial  destruction  of  the  body-substance,  two  im- 
portant conclusions  may  be  deduced  from  the  observations  before  us. 
In  the  first  place,  the  proposition  follows,  that,  like  muscle,  the  sub- 
stance of  iwotozoa  obeys  a  law  of  'polar  excitation,  in  wliieli,  Iwioever,  the 
localisation  (polar  distribution)  of  effects  is  reversed — excitation  being 
at  the  anode  at  onake,  at  the  kcdhode  cd  brecdc,  of  current.  Secondly, 
the  fact  carries  conviction,  that  the  process  of  excitation  is  effected 
not  merely  at  the  moment  of  commencement  and  cessation  of  citrrent, 
but  proceeds  throughoid .  the  whole  period  during  %Dhich  the  current 
is  passing,  and  for  a  short  time  after  it  has  been  broken.  This 
excitation  does  not  produce  contraction  as  in  muscle,  but  sets  up 
a  centripetal  backward  flow  of  the  protoplasm,  which  under 
certain  conditions  may  lead  to  local  destruction  of  the  outermost 
layers.  The  various  phenomena  connected  with  the  final  disinte- 
gration in  various  forms  are  sufficiently  intelligible  from  the 
different  composition  and  consistence  of  protoplasm  in  each 
particular  case.  Under  certain  conditions — e.g.  in  Amoeba — 
visible  changes  of  form  are  altogether  absent;  the  excitation  remains 
"  latent."  But  even  then  the  direction  of  movement  of  the 
entire  body-mass  gives  cogent  evidence  of  the  existence  of  polar 
excitation,  and  it  is  quite  intelligible  that  such  excitation  should, 
under  certain  conditions,  give  rise  to  an  axial  disposition  of  the 
body   of  the   proteid.      In   the    first   place,   we    find   that  other 


in  ELECTRICAL  EXCITATION  OF  MUSCLE  307 

stimuli,  e.g.  light,  warmth,  chemical  reagents,  are  known  to 
exercise  a  directive  influence,  if  they  act  locally,  or  with  differ- 
ent intensity  at  different  parts  of  the  excitable  substance. 
Certain  light  rays  (those  with  short  vibrations  in  particular) 
cause  many  of  the  Flagellata,  as  well  as  the  spores  of  many 
Algae,  to  move  in  the  direction  of  the  rays  that  strike  them,  either 
from  or  towards  the  light  (positive  and  negative  heliotropism). 
Pfeffer  has  demonstrated  an  analogous  effect  of  chemical  reagents 
in  solution  upon  Bacteria  and  Flagellata,  i.e.  attraction  or  repul- 
sion of  the  organisms,  a  chemotropic  action  positive  or  negative. 
In  all  these  cases,  as  Verworn  correctly  remarks,  we  have  to  do 
with  some  j)olar  excitation  of  the  protozoa,  that  gives  rise  to  an 
axial  orientation  of  the  organism  in  accordance  with  the  direction 
of  excitation,  or,  more  correctly  speaking,  of  the  differences  in 
intensity  of  such  excitation.  On  the  assumption  that  when 
current  passes  through  an  amoeba,  the  make  excitation,  as  in 
other  rhizopods,  is  primarily  anodic,  it  is  evident  that  a  formation 
of  pseudopodia  due  to  a  forward  current  of  the  protoplasm  can 
take  place  only  in  the  direction  of  the  kathode ;  the  forward 
movement  in  the  direction  of  the  current  is  thus  accounted  for. 

This  directive  action  of  the  current  ("  Galvanotropism ")  is 
still  plainer  in  the  case  of  many  rapidly-moving  ciliated  Infusoria, 
e.g.  Flagellata.  If  a  few  drops  of  hay  infusion  swarming  with 
Paramecium  are  placed  between  clay  electrodes  (as  described 
above)  upon  an  object-glass,  and  traversed  by  a  sufficiently  strong 
current,  the  following  effects  (as  pointed  out  by  Verworn)  are 
observed,  either  with  the  naked  eye  or  with  a  magnifying  lens. 
"  At  closure  the  Paramsecia  turn  altogether  as  if  at  word  of  com- 
mand, with  the  anterior  pole  of  the  body  towards  the  negative 
electrode,  and  swim  in  this  direction  with  uniform  speed " 
(Fig.  99). 

In  a  short  time  the  anodic  side  of  the  drop  is  completely 
cleared  of  Paramsecia,  not  one  being  left  behind ;  the  whole  mass 
has  crowded  to  the  kathode.  As  long  as  the  circuit  is  closed  the 
protozoa  remain  thus ;  if  the  current  is  broken  the  paramecia 
turn  instantly  with  their  anterior  ends  towards  the  anode,  and 
swim  away  in  this  direction.  The  kathode  is  quickly  deserted, 
and  the  majority  of  the  organisms  are  now  collected  round  the 
.  anode.  The  crowding  is,  however,  by  no  means  so  complete  as 
that  produced  at  the  kathode  by  make  of  the  current,  and  the 


308 


ELECTRO-PHYSIOLOGY 


paramsecia  soon  begin  to  swim  about  in  all  directions,  and  in  a 
short  time  are  once  more  uniformly  distributed  throughout  the 
drop.  This  manoeuvre  is  repeated  as  often  as  the  current  is 
closed,  with  the  same  precision. 

It  is  easy  to  prove  that  the  living  state  is  an  essential  condi- 
tion of  these  phenomena  by  repeating  the  experiment  after  killing 
the  animals  with  ether  or  chloroform. 

If  unpolarisable  electrodes  are  used  with  points  of  baked  clay 
dipping    into    the    infusion,  instead   of  the   excitation    chamber 


Fig.  99. — Galvanotropism  of  Paranicecium  aurclia.    (Verworn.) 

described  above,  the  effects  are  very  curious.  At  closure  of  the 
current  all  the  paramsecia  arrange  themselves  longitudinally,  in 
accordance  with  the  current  curves,  and  swim  along  these  lines 
towards  the  kathode,  so  that  those  which  happen  to  be  at  the 
outer  part  of  the  drop  follow  an  almost  semicircular  course. 
If  the  current  is  frequently  reversed,  the  paramaecia  may  be 
driven  now  in  one  direction,  now  in  the  other.  As  may  readily 
be  understood,  very  rapid  alternations  of  current  do  not  cause 
them  to  travel  in  a  definite  direction,  nor  give  rise  to  any  polar 
accumulation.  A  ijriori  there  can  be  no  doubt  that  in  this  case, 
as    in    that    of  Amoeba,  we   have   to    do  with  a  "  galvanotropic 


Ill  ,  ..      ELECTRICAL  EXCITATIOX  OF  ifUSCLE  309 

action  "  due  to  latent  make  excitation  at  the  anode ;  and  the  fact 
itself  is  directly  demonstrable  by  corresponding  experiments  on 
other  infusoria  less  resistant  to  the  action  of  current  than  Para- 
msecium  aurelia.  On  Paramecium  bursaria  (the  galvanotropic 
reaction  of  which  to  weak  currents  is  as  well  marked  as  is  that 
of  Paramaecium  aurelia),  Yerworn,  using  strong  currents,  suc- 
ceeded, as  in  the  case  of  the  above-mentioned  rhizopods,  in 
producing  a  visible  destruction  of  one  pole  of  the  body,  i.e.  of  the 
anodic  pole,  that  is  posterior  when  swimming  takes  place.  At 
closure  of  the  current  the  first  effect  is  as  usual  an  axial  orienta- 
tion, and  subsequently  as  the  proteid  begins  to  swim  over  towards 
the  kathode,  a  hyaline  mass  protrudes  from  the  posterior  end  and 
gradually  enlarges.  It  can  hardly  be  doubted  that  this  is  analo- 
gous to  the  anodic  disintegration  that  occurs  in  Actinosphserium 
and  Pelomyxa.  It  is  still  easier  to  bring  about  a  similar  reaction 
in  the  case  of  Bursaria  trunculata ;  moderately  strong  currents 
are  sufficient  to  effect  a  granular  disintegration  of  the  anodic  end 
of  the  body,  which  increases  as  long  as  the  circuit  remains  closed, 
until  the  whole  animal  is  converted  into  a  granular  mass  loosely 
held  together  by  glutinous  material.  These  large  and  more 
resistant  infusoria  have  no  time  to  adjust  their  axis,  especially 
with  strong  currents,  but  the  destruction  begins  at  any  aspect  of 
the  body  which  happens  to  be  turned  towards  the  anode  at  the 
moment  of  closure  (Yerworn). 

A  large  number  of  other  ciliated  Infusoria,  also  some  of  the 
riagellata  (Feridinium  tahulatuin  and  TracJielomonas  Mspida),  as 
investigated  by  Yerworn,  behave  in  a  similar  manner.  On  the 
other  hand,  in  some  other  protozoa,  the  current  produces  a 
precisely  opposite  directive  effect.  If  the  swimming  or  crawling 
movements  towards  the  kathode  be  designated  as  negative  gal- 
vcinotroinsm,  the  reverse  effect  (anterior  end  to  anode,  and 
movement  in  that  direction)  maybe  caMed  j^ositive  gcdvcmotrojnsiii. 
Yerworn  found  this  last-named  effect  in  Opalina  ranarum,  also  in 
certain  Flagellata,  Polytoma  uvella  and  Cryptornonas  erosa  in 
particular.  The  phenomenon  described  hj  A'^erworn  as  "  transverse 
galvanotropism "  is,  moreover,  remarkable ;  certain  very  elongated 
Infusoria  (e.g.  Spirostomum  amhiguum,  2  mm.  long)  place  them- 
selves with  their  long  axis  at  right  angles  to  the  lines  of  current 
(perhaps  in  consequence  of  a  failure  of  excitation  by  transverse 
currents).     Apart  from  these  isolated  cases,  which  require  further 


310  ELECTRO-PHYSIOLOGY 


study,  it  is  allowable  to  suppose  that  the  proposition  laid  down 
above  with  reference  to  the  electrical  excitation  of  protozoans  holds 
good  for  the  great  majority  of  the  forms  hitherto  investigated, 
thus  establishing  in  their  case  a  peculiar  and  unquestionably  very 
remarkable  opposition  to  the  phenomena  of  muscular  elements  in 
general,  as  well  as  of  nerve.  The  allied  assumption  that  the  law 
of  polar  excitation,  according  to  Pfliiger,  holds  good  without 
exception  for  all  excitable  protoplasm,  thus  appears  to  be  finally 
disposed  of. 

The  interesting  observations  of  Eoux  (48)  upon  "  moiyho- 
logical  polarisation "  of  ova  are  germane  to  the  phenomena 
described  in  the  foregoing  pages.  In  order  to  determine  whether 
the  electrical  current  was  capable  of  influencing  the  direction  of 
the  first  cleavage  of  the  ovum,  Eoux  submitted  a  strip  of  frog's 
spawn  about  4  cm.  long,  with  fertilised  ova,  to  the  action  of  an 
alternating  current  of  100  volts  potential,  intended  for  lighting 
purposes.  In  about  ten  minutes  a  transverse  furrow  dividing 
the  egg  into  two  equal  parts  appeared  in  each  egg,  the  furrow 
being  everywhere  at  right  angles  to  the  direction  of  current. 
Even  before  this  happens  a  distinct  partition  of  the  surface  into 
three  fields  is  noticeable,  divided  off  by  two  parallel  circular 
boundary  lines,  an  equatorial  girdle  without  visible  alteration, 
and  two  polar  arete  opposite  the  electrodes,  with  an  altered  and 
coloured  surface.  If  instead  of  a  single  band  of  spawn  a  simple 
layer  covering  the  bottom  of  a  round  vessel  is  submitted  to  the 
action  of  the  current,  the  electrodes  being  placed  at  its  two 
opposite  margins,  the  equatorial  girdle  of  the  entire  series  of 
eggs,  or,  more  precisely  speaking,  the  boundary  lines  between 
it  and  the  polar  zones,  form  curves  which  all  begin  at  right 
angles  to  a  straight  line  between  the  electrodes  (Fig.  100),  and 
then  sweep  round  the  nearer  electrode,  gradually  increasing  their 
distance  from  it  as  they  approach  the  wall  of  the  vessel,  to  end 
at  right  angles  to  the  same. 

The  amount  of  curvature  is  at  its  maximum  close  to  the 
electrodes,  and  gradually  diminishes  up  to  the  middle  line,  at 
right  angles  to  the  current  axis.  The  merest  inspection  shows 
us  that  we  are  here  dealing  with  lines  of  equal  potential,  or  the 
equipotential  surfaces  of  the  whole  electrical  field  marked  out 
by  these.  In  the  ova  corresponding  with  a  single  line  of 
potential,  the   breadth  of  the   equatorial   surface   increases  with 


ELECTRICAL  EXCITATION  OF  MUSCLE 


311 


its  distance  from  the  straight  line  between  the  electrodes,  so 
that  the  ova  in  immediate  contact  with  the  margin  present  the 
least  polar  zones,  and  the  largest  equatorial  surface.  Bearing 
in  mind  the  reaction  of  each  single  ovum  to  the  alternating 
current,  a  certain  analogy  with  the  effects  above  described  in 
Actinosphasrium  cannot  be  disputed,  and  if  two  protozoa  are 
conceived — of  the  size  of  frog's  ova,  and  submitted  under  similar 
conditions  to  the  action  of  the  alternating  current- — the  middle 
disc  remaining  over,  when  the  polar  zones  had  disintegrated, 
would  presumably  exhibit  an  arrangement  of  the  lines  of 
potential,  corresponding  with  the  equators  of  the  ova  in  Eoux's 
experiment. 

But  this  conformity 
further  extends  to  the  dif- 
ference in  mode  of  action 
at  either  pole,  which  of 
course  appears  only  with 
uniform  currents.  At  uni- 
form conditions  of  experi- 
ment, there  is  developed — 
as  Eoux  pointed  out — in 
ripe,  unfertilised  ova,  "  a 
large  grayish  polar  zone, 
round  the  positive  elec- 
trode, directed  towards  the 
anode,  extending  far  be- 
yond the  middle  line  of 
the  electrical  field,  while 
only  the  two  rows  of  ova  lying  nearest  the  kathode  had  a 
coloured  kathodic  polar  zone  in  default  of  an  anodic  zone."  This 
last  always  appears  later,  and  the  changes  are  less  than  in  the 
positive  zones.  With  weaker  currents,  no  polar  zone  appears  on 
the  negative  side  of  the  ovum. 

If  these  effects  of  current  cannot  be  termed  direct  con- 
sequences of  an  electrical  excitation  of  the  plasma  of  the  ovum; 
they  do  undoubtedly  represent  a  specific  reaction  of  the  still 
living,  or  at  least  approxmiately  normal,  ovum,  even  when  the 
capacity  of  development  is  not  necessarily  preserved.  Eoux 
was  enabled  to  demonstrate  formation  of  polar  zones  in  masses  of 
freshly  extruded  unsegmented  ova. 


Fig.  100.— Ova  of  Frog  in  vessel  of  water,  traversed  by 
current  from  the  two  straight  lines,  marking  the 
vertical  electrodes.    Polar  fields  darlc.    (Koux.) 


312  ELECTRO-PHYSIOLOGY  chap. 

The  reaction  of  ova,  which  are  already  at  different  stages  of 
segmentation,  is  also  interesting.  Both  in  the  ovum  divided  into 
two  or  more  cells  (Fig.  101),  as  in  the  morula  stage,  and  again 
in  the  blastula,  consisting  of  many  little  cells,  each  single  cell 
of  the  surface  shows  "  special  polarisation "  when  the  whole 
organism  is  submitted  to  current,  inasmuch  as  "  the  cells  lying 
only  on  the  polar  side  of  the  ovum  exhibit  one  polar  zone,  which 
is  visible  externally,  while  the  equator  takes  up  the  free  surface 
of  the  cell  lying  distal  to  the  pole."  Further  differentiation  into 
smaller  and  fewer  cells,  in  older  blastuhe  and  the  gastrula,  will, 
however,  under  the  same  conditions,  once  more  bring  about  a 
collective  equator  between  two  collective  polar  zones,  since  a 
girdle  from  the  poles  to  the  farthest  cells  remains  unaltered. 
The  special  polarisation  of  single  cells  in  the  early  stages  of 
segmentation  would  appear  to  be  "  bound  up  with  a  property 
which  diminishes  with  their  vitality,"  inasmuch 
as  each  attack  which  weakens  the  vital  energy 
of  the  ovum  also  prevents  the  formation  of 
special  polar  zones,  wholly  or  partially,  without. 
Fig.    101.  — "Special  i^jQwever,  effecting  the  characteristic  "  total  polar- 

polarisation     of  an  '  "  '- 

ovum  in  four  seg-  isatioii "  of  the  entire  cell  aggregate.     Thus  Eoux 
tTaction^of  stroiT"-  remarked   in  segmented  ova  treated  with  weak 
'alternating  cur-  carbolic  acid,  wMch  produccd  no  change  of  form 
externally,  that  while  special  polar  zones  appeared 
at  the  first  moment  of  action  of  the  current,  they  spread  rapidly 
over  the  whole  surface  of  the  cell  directly  exposed  to  the  cur- 
rent, so  that  on  each  side  "  a  single  polar  zone,  springing,  bow- 
ever,  in    the    upper    hemisphere    from    rounded    cells,  appears ; 
while  the  "  general  equator,"  marked  off  by  two  parallel  sectors, 
lies    between    them.       With    stronger    application    of   the    acid 
there  is  no  reaction.       Similar  changes  are  effected  by  various 
temperatures. 

If  unsegmented  ova,  or  moruh'e,  are  left  in  water  for  a  short 
time  at  39—45°  C.  the  reactions  are  considerably  increased, 
while  longer  exposure  to  heat  has  an  opposite  effect — the  morula 
no  longer  exhibiting  special  polar  zones,  but  only  the  two  "  general 
polar  zones  "  separated  by  one  equator.  These  results,  along  with 
the  further  fact,  that  on  cooling  the  ova  the  reaction  to  current 
is  considerably  retarded,  indicate  that  we  are  in  presence  of  a 
vital  phenomenon,  of  which  the   further  investigation  promises 


Ill  .         ELECTRICAL  EXCITATION  OF  MUSCLE  313 

to  contribute  largely  to  our  knowledge  of  the  nature  of  the  polar 
working  of  the  current. 

SUMMAEY 

Gathering  up  the  results  of  these  detailed  investigations 
into  the  visible  effects  of  electrical  excitation  in  different  con- 
tractile substances,  certain  points  of  view  present  themselves 
from  which  it  appears  possible  at  least  to  conjecture  the  specific 
action  of  current. 

In  the  first  place,  it  must  be  remarked  that  the  laiv  of 
excitation  which  du  Bois-Eeymond  postulated  as  universal  (only, 
it  is  true,  with  regard  to  the  electrical  excitation  of  motor  nerves, 
but  which  was  subsequently  applied  to  the  direct  excitation  of 
contractile  substances  also)  is  not  found  to  be  a  correct  repre- 
sentation of  fact.  It  cannot  therefore  be  taken  as  the  basis  of 
theoretical  conclusions  in  regard  to  the  specific  nature  of  electrical 
excitation.  The  law  in  its  original  form  was  as  follows  :  "  The 
motor  nerve  (or  muscle,  contractile  protoplasm)  responds  by  the 
twitch  of  the  muscle  belonging  to  it  (or  other  excitatory  symp- 
tom), not  to  the  absolute  value  of  current  density  at  the  moment, 
but  to  the  alterations  of  this  value  from  one  moment  to  an- 
other— the  stimulus  to  movement  consequent  on  these  changes 
being  greater  in  proportion  to  their  rapidity  at  uniform  magni- 
tude, or  amount  per  unit  of  time." 

Even  if  we  admit  that  in  many  cases,  particularly  in  all  quickly 
reacting  and  quickly  conducting  contractile  substances,  the  effect  of 
excitation  (so  far  as  it  is  expressed  by  visible  change  of  form)  is 
especially  prominent  at  the  moment  when  current  is  made  or 
broken  (closure  and  opening  twitch),  there  cannot  on  the  other 
hand  be  the  slightest  doubt  that  the  electrical  current  in  every 
case  produces  during  its  entire  closure  that  change  in  the  irritable 
substance  which  is  fundamental  on  the  one  hand  to  excitation,  and 
on  the  other  to  antagonistic  inhibitory  processes.  In  many  cases 
these  continuous  effects  are  the  only  consequence  of  electrical 
excitation  {e.g.  smooth  muscle,  many  protozoa).  Currents  of 
insufficient  duration  are  ineffective,  as  may  be  demonstrated  on 
striated  muscle  by  the  application  of  various  methods  {supra). 
Under  all  conditions  the  current,  in  order  to  excite,  must  have 
a    certain    period   of  duration — greater  in   proportion   with    the 


314  ELECTRO-PHYSIOLOGY 


lower  excitability  and  slower  reaction  of  the  protoplasm  in 
question.  And  as  at  make  of  the  current  the  excitation  by 
no  means  accompanies  the  moment  of  closure  only,  so  too  at  break 
the  opening  excitation  considerably  outlasts  the  disappearance  of 
the  current. 

The  capital  importance  attaching  to  the  manifestation  of 
the  make  and  break  twitch  in  striated  muscle,  with  regard 
to  the  entire  theory  and  discussion  of  current  action,  renders 
it  advisable  once  more  to  raise  the  question  of  what  con- 
ditions are  essential  to  the  initiation  of  a  wave  of  contraction. 
We  know  from  experiment  that  in  order  to  produce  a  wave,  i.e. 
a  perceptible  twitch  of  the  entire  longitudinally  traversed  muscle, 
the  magnitude  of  the  stimulus  must  exceed  a  certain  minimal 
limit.  If  the  stimulus  is  too  weak  the  contraction  either  remains 
localised,  or  spreads  over  a  limited  area  only  of  the  muscle  by 
conduction  from  section  to  section,  until  it  finally  dies  away  in 
consequence  of  the  "  decrement."  The  second  condition  essential 
to  the  propagation  of  excitation  is  a  certain  rapidity  of  process 
of  the  required  magnitude.  The  changes  at  the  seat  of  direct 
excitation  must  suddenly  reach  a  corresponding  magnitude,  after 
which  excitation  transmits  them  to  the  neighbouring  sections, 
and  these  in  turn  produce  the  same  effect  upon  their  neighbours. 
That  this  is  so  is  proved  directly  by  the  fact  that  it  is  easy  to 
pass  a  strong  galvanic  current  into  a  muscle  without  any  visible 
excitation  phenomena,  which  no  doubt  is  partly  due  to  the 
gradual  increase  of  local  fatigue  at  the  kathode.  This  applies 
not  merely  to  the  electrical  make  and  break  twitch,  but  to 
many  other  experiments.  We  need  only  refer  to  the  fact  that 
mechanical  excitation  caused  by  pressure  does  not  produce  a 
muscle  twitch  if  it  is  increased  gradually. 

This  all  throws  light  upon  the  true  significance  of  du 
Bois'  law  of  excitation,  since  it  shows  that  not  merely  the 
locccl  changes  at  the  seat  of  excitation,  but  still  more  the 
pro2Jagation  of  the  excitatory  process,  i.e.  the  discharge  of  a 
wave  of  excitation  (contraction),  are  dependent  upon  the  varia- 
tions of  current  intensity,  and  the  steepness  of  the  same,  in  the 
case  of  tissues  in  which  conductivity  is  adequately  developed. 
The  "  universal  law  of  excitation "  refers  therefore  less  to 
the  manner  of  the  excitatory  process,  and  effectuation  of  the 
changes    of  the    excitable   substance   fundamental   to   it,    at   the 


Ill  ,  ,-  ELECTRICAL  EXCITATION  OF  MUSCLE  315 

scat  of  direct  excitation  (physiological  anode  and  kathode), 
than  to  the  conditions  of  the  propagation  of  the  excitatory 
process  by  conduction.  In  this  sense  the  law  may  be  expressed 
as  follows  : — 

As  a  rule,  when  current  is  cqjj^liecl  to  suitable  objects,  trcms- 
mission  of  excitatiori  from  the  'jpoint  directly  stimvlatcd  occurs  only 
with  sufficiently  rapid  cdtcrations  of  current,  vjhether  starting  from 
zero,  or  from  any  given  vcdue. 

Comparative  investigation  of  different  contractile  substances 
shows  directly  that  visible  changes  arise  at  the  point  of 
excitation  during  the  entire  passage  of  current,  and  for  some 
time  after,  the  significance  of  which  is  clear  except  in  cases 
where,  e.g.  in  striated  muscle,  they  are  more  or  less  over- 
shadowed by  the  results  of  the  transmitted  excitation  ("  twitch  "). 
Without  entering  into  the  question  why  there  is,  as  a  rule,  only 
one  wave  of  contraction  at  closure,  and  opening,  of  the  circuit,  it 
•  may  be  pointed  out  that  the  same  effect  occurs  under  certain 
conditions  with  intermittent  persistent  excitation  from  homo- 
dromous,  rapidly  interrupted  currents,  just  as  in  other  cases  the 
continuous  closure  of  a  battery  current  will  produce  a  persistent 
excitation  of  the  entire  muscle  similar  in  appearance  to  that 
caused  by  intermittent  excitation.  As  regards  the  first,  it  was 
shown  by  Bernstein  and  Engelmann  that  when  the  interval 
between  two  consecutive  closures  of  a  rapidly  interrupted  battery 
current,  falls  below  a  certain  value,  the  effect  of  excitation  upon 
striated  muscle  is  similar  to  that  produced  by  closure  of  a  con- 
stant current ;  i.e.  a  single  wave  of  contraction  (initial  twitch) 
starts  from  the  kathode,  at  which,  as  in  persistent  closure,  there 
may  be  persistent  local  contraction.  The  magnitude  of  this 
interval  diminishes  with  increasing  strength  of  current,  and 
increases  with  diminishing  excitability. 

The  same  fact  is  still  more  easily  demonstrated,  according  to 
Engelmann,  upon  the  sluggishly  reacting  ureter,  since  the  pauses 
between  two  consecutive  closing  stimuli  may  be  much  greater  than 
in  striated  muscle  without  alteration  of  the  effect,  inasmuch  as  a 
wave  of  contraction  only  occurs  at  the  beginning  and  end  of  the 
intermittent  excitation,  starting  in  the  one  case  from  the  kathode, 
in  the  other  from  the  anode  ("  initial  and  final  twitch  ").  Under  all 
conditions  a  certain  interval,  varying  greatly  in  different  contractile 
substances  (where  conductivity  is  in  general  more  highly  developed), 


316  ELECTRO-PHYSIOLOGY 


is  required  before,  when  one  wave  of  contraction  has  expired,  those 
conditions  are  restored  which  are  essential  for  bringing  about  a 
new  wave  of  excitation  (Engehnann). 

The  facts  submitted  above  re  discharge  of  a  rhythmical 
succession  of  contraction  waves  during  protracted  closure  of  a 
batterj  current,  do  not  contradict  this  conclusion.  Expressed  in 
general  terms,  the  recovery  of  an  original  state  of  the  excitable, 
conducting  substance  takes  place  only  when  a  new  wave  of 
contraction  passes  during  the  continuance  of  an  uninterrupted 
stimulus. 

Yet,  in  so  far  as  the  ratio  and  time-relations  of  the  assimilatory 
and  dissimilatory  processes  in  living  matter  are  correlative,  this 
would  apply  to  intermittent,  as  well  as  to  uninterrupted,  causes  of 
excitation.  As  regards  the  latter  we  need  only  refer  to  the  wide 
distribution  of  rhythmical  processes  of  movement,  depending,  as 
may  be  shown,  in  many  cases  upon  the  capacity  of  certain  kinds  of 
protoplasm  to  convert  a  constant  stimulus  into  rhythmical  excita- 
tion. This  capacity  is  more  or  less  developed  from  the  relatively 
undifferentiated  protoplasm  of  protozoa  (contractile  vacuoles)  up 
to  striated  muscles,  but  with  striking  differences  of  degree.  Thus 
the  non-ganglionated,  cardiac  muscle  pulsates  rhythmically  not 
merely  with  uniform  mechanical  or  chemical  stimuli,  but  also 
under  the  action  of  the  constant  current,  and  the  same  applies, 
though  in  a  much  lesser  degree,  to  striated  skeletal  muscle. 
Without  entering  on  the  question  of  the  specific  cause  of  the 
rhythm  in  these  and  similar  cases,  w^e  may  point  out  that  the 
occurrence  of  a  rhythmical  succession  of  contractions  during 
sustained  closure  of  the  current  is  a  very  convincing  proof  that 
the  excitation  process  is  persistently  maintained  during  electrical 
stimulation.  The  electromotive  effects  of  sending  current  into 
the  muscle,  known,  after  du  Bois,  as  secondary  electromotive 
manifestations  (which  will  be  discussed  below),  are  also  of  great 
importance  in  this  connection. 

The  second  fundamental  proposition  is  the  law  of  the  exclus- 
ively polar  action  of  every  ordinary  electriccd  current,  to  the  effect  that 
the  excitatory  process  is  ijrimarily  discharged  at  the  physiological 
kathode  only  {in  the  majority  of  cases)  at  and  during  closure  of  the 
exciting  current,  at  the  p)hysiologiccd  anode  only,  at  and  subsequently 
to  hreah  of  the  current.  A  remarkable  exception  in  localisation  of 
electrical  excitation  is  however  shown  to  exist  in  many,  perhaps 


Ill  ELECTRICAL  EXCITATION  OF  MUSCLE  317 

most,  protozoans,  where  the  excitation  is  indeed  conspicuously  polar, 
but  appears  at  closure  to  be  localised  at  the  anode,  on  opening 
the  current  at  the  kathode ;  and  Eoux's  observations  upon  the 
morphological  "  polarisation  "  of  ova  also  fall  under  this  category. 
Further,  in  many  cases  an  equally  marked  inhibitory  action  of  the 
current  is  exhibited  in  corresponding  changes  of  form,  which 
appear  simultaneously  with  the  manifestations  of  excitation,  but 
are  localised  at  the  opposite  pole.  Kathodic  closure  excitation  there- 
fore implies  a  simultaneous  anodic  closure  inhihition,  anodic  hreah 
excitation,  kathodic  break  inhihition.  Thus  both  the  simultaneous 
polar  effects,  or  after-effects,  of  current,  and  the  subsequent  effects 
at  tlie  same  pole,  as  a  rule,  exhibit  an  antagonism  (as  is  more 
particularly  expressed  in  the  opposite  reactions  of  "  electrotonic  " 
changes  of  excitability  at  the  physiological  poles)  by  which  it  is 
possible  to  demonstrate  the  inhibitory  effects  even  in  such  cases 
where,  failing  a  tonic  state  of  excitation,  no  visible  alteration  of 
form  appears.  So  far  as  may  be  concluded  from  experiments  on 
muscle,  the  current,  provided  its  strength  does  not  exceed  certain 
limits,  appears  to  traverse  the  intrapolar  area  without  producing 
any  perceptible  alterations  within  it.  Under  some  conditions 
excitation  phenomena  appear  in  the  vicinity  of  the  physiological 
pole  during  closure  of  the  anode  and  after  opening  the  kathode ; 
but  these  seem  to  be  due  to  diffusion  of  current  and  formation 
of  secondary  electrode  points,  and  are  accompanied  by  simul- 
taneous, antagonistic  changes  (inhibition)  in  the  region  of  the 
other  pole. 

The  persistence  of  the  excitatory  or  inhibitory  effect  of  current 
during  closure,  as  well  as  the  localisation  and  antagonism  at  the 
poles,  prove  incontestably  that  the  consequences  of  electrical  excita- 
tion are  only  a  specicd  manifestation  of  commencing  electrolysis  in 
the  living  substarice.  On  this  assumption  it  becomes  intelligible 
that  the  anodic  and  kathodic  alterations  should  neutralise  each 
other  when  produced  by  a  transverse  current  at  the  opposite 
longitudinal  margins  of  a  muscle-fibril,  or  any  minute  tract  of 
contractile  substance  (e.g.  a  pseudopodium).  This  view  is  not 
contradicted  by  the  fact  that  in  certain  kinds  of  protoplasm  the 
changes  which  underlie  the  excitation  appear  to  be  localised  not 
at  the  kathode,  but  conversely  at  the  anode ;  for  this  is  ob- 
viously dependent  on  the  quality  of  the  excitable  substance,  which 
is  not  necessarily  the  same  in  all  cases.     These  brief  observations 


318  ELECTRO-PHYSIOLOGY  chap. 

must  suffice  for  the  present.  The  subject  will  be  taken  up  again 
in  connection  with  the  theory  of  electrical  excitation,  in  so  far  as 
it  is  possible  to  formulate  any  such  propositions. 

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29.  W.  BiEDEEMANN.     Pfliigers  Arch.     XLVI.     1890.     p.  398. 

30.  M.  FuEST.     Pfliigers  Arch.     XLVI.     1890.     p.  367  ff". 

31.  W.  BiEDEEMANN.     Pfliigers  Arch.     XLV.     1889.     p.  369. 

32.  ScHiLLBACH.     Virchows  Arch.     1887.     p.  109. 

33.  LiJDEEiTZ.     Pfliigers  Arch.     XLVIII.     p.  1  fl". 

34.  HiLLEL  JoFE.     Recherches  physiologiques  sur  Taction  polaire  des  courants 

electriques.     These  inaug.     Geneve  1889. 

35.  W.  BiEDEEMANN.      Beitrage   zur   allgem.    Nerven-    und   Muskeiphysiologie. 

XIV.      (Sitzungsberichte  der  Wiener  Academie.      LXXXIV.      III.   Abth. 
1884.) 

36.  Beitrage  zur  allgem.  Nerven-  und  Muskeiphysiologie.    XVIII.     (Sitzungs- 
berichte der  Wiener  Academie.     XCII.     III.  Abth.     1885.) 

37.  W.  KxJHNE.     Arch,  fiir  Anat.  und  Physiol.     1860.     p.  542. 

38.  E.  DU  Bois-Reymond.     Gas.  Abhandlungen.     I.     p.  126. 

39.  L.  Hermann.     Pfliigers  Arch.     XXXIX.     p.  603. 

40.  Jendeassik.     Du  Bois  Arch,  fiir  Physiol.     1879.     p.  300. 

41.  Regeczy.     Pfliigers  Arch.     XLV. 

42.  L.  Hermann.     Pfliigers  Arch.     XXX. 

43.  R.  Heidenhain.     Physiolog.  Studien. 

44.  J.  Rosenthal.     Zeitschr.  fiir  rat.  Med.     3.     III.     p.  132. 

45.  Hermann's  Handbuch  der  Physiologic.     I.     1.     p.  365  ff'. 

46.  W.  KiJHNE.     Untersuchungen  iiber  das  Protoplasma.     Leipzig  1864. 

47.  M.  Verworn.     Pfliigers  Arch.     XLV.  und  XLVI. 

48.  Roux.     Sitzungsberichte  der  Wiener  Academie.     CI.     III.  Abth.     1892. 


CHAPTEE   IV 

ELECTROMOTIVE    ACTION    IN    MUSCLE 

The  potential  energy  stored  as  chemical  force  in  muscle,  as  in 
all  other  living  tissue,  yields  in  general  three  forms  of  vital 
energy,  i.e.  mechanical  work  (mass  motion)  and  molecular  motion 
in  heat  and  electricity.  In  so  far  as  muscle-cells  proper  are 
concerned  it  is  the  first  of  these  which  plays  the  weightiest 
part,  and  must  be  regarded  as  their  characteristic  function.  The 
production  of  heat  is  not  nearly  as  conspicuous  in  comparison, 
although  in  warm-blooded  animals  it  also  plays  an  important  part 
in  the  economy  of  the  organism.  Finally,  the  development  of 
electricity,  which  alone  concerns  us  in  the  present  connection, 
falls,  with  a  few  negligible  exceptions,  so  far  behind  the  other 
two  forms  of  living  energy  that  the  most  refined  methods  and 
delicate  instruments  are  needed  in  order  even  to  ascertain  its 
existence.  That,  notwithstanding  such  disadvantages,  this  chapter 
of  electro-physiology  should  be  among  the  best  known  and  most 
carefully  worked  out  in  Physiology  is  mainly  due  to  the  fact  that 
since  the  discovery  of  the  marvellous  action  of  the  electrical 
current  upon  excitable  parts  of  the  body,  and  the  epoch-making 
controversy  between  Galvani  and  Volta,  the  idea  that  the  mys- 
terious phenomena  of  muscular  and  nervous  activity  were  in  some 
degree  related  to  the  no  less  obscure  force  of  electricity  never 
wholly  vanished.  Although  the  conviction  subsequently  obtained 
that  the  force  which  travels  from  nerve  to  muscle  (the  "  nervous 
principle  ")  is  not  in  itself  electricity,  the  rapid  additions  to  the 
theory  of  electromotive  action  in  certain  animal  tissues,  and  in 
muscle  and  nerve  in  particular,  kept  alive  the  presumption  that 
these  manifestations  cannot  be  without  import  for  the  function  of 
the  parts  in  which  they  are  exhibited. 


CHAi'.  IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  321 

Soon,  however,  in  spite  of  innumerable  labours  and  discoveries 
in  this  well-worked  field,  a  marked  contradiction  asserted  itself 
between  the  sum  of  theoretical  and  experimental  data,  and  the 
almost  total  ignorance  of  their  significance  for  the  function  of 
the  tissues  involved :  here  we  are  not  yet  emancipated  from  the 
stage  of  more  or  less  well-founded  conjecture.  In  striking  con- 
trast, on  the  other  hand,  is  the  electrical  development  in  the 
living  organs  of  those  wonderful  fishes,  armed  with  powerful 
batteries,  which  afford  a  solitary  illustration  of  the  manner  in 
which  from  insignificant  beginnings  in  muscle  or  gland  cells, 
where  the  electromotive  action  is  hard  to  demonstrate,  organs 
have  been  developed  whose  function  as  powerful  electrical  weapons 
of  attack  and  protection  is  unmistakably  attested.  The  import- 
ance of  these  facts  cannot  be  neglected,  and  the  interest  manifested 
in  the  department  of  electro-physiology  now  before  us  is  the  more 
legitimate,  since  the  fundamental  researches  of  Matteucci,  du 
Bois-Eeymond,  L.  Hermann,  and  others  provide  a  basis  which  is 
not  merely  a  satisfactory  starting-point  for  future  labours,  but 
from  exactness  of  method  guarantees  the  true  interpretation  of 
all  such  observations.  Notwithstanding  the  importance  which 
attaches  to  the  historical  development  of  the  subject,  it  cannot  be 
entered  on  here,  and  indeed  could  only  be  abbreviated  from  the 
masterly  review  'given  by  du  Bois-Eeymond  in  his  classical 
"  Untersuchungen." 

We  shall  therefore  proceed  at  once  to  the  description  of 
electromotive  action  in  the  "  resting  "  muscle. 

I. CUEREXT    OF    EeST    IN    MuSCLE 

Between  1840-1843  it  was  discovered  almost  simultaneously 
by  C.  Matteucci  and  E.  du  Bois-Eeymond  that  isolated,  striated 
muscle,  under  certain  conditions,  exhibited  pronounced  and 
regular  electromotive  activity.  This  opened  up  a  vast  field 
of  electro -physiology,  the  further  investigation  of  which  will 
always  stand  out  as  an  admirable  achievement  of  du  Bois- 
Eeymond,  after  whom  Hermann  has  made  the  greatest  con- 
tributions. If  a  long  strip  is  cut  out  of  the  middle  of  a  frog's 
muscle  with  parallel  fibres  and  regular  structure  {e.g.  sartorius, 
gracilis,  semimembranosus),  a  so-called  muscle-prism,  or  muscle 
cylinder,  is   obtained,   where   two   end -surfaces    are    formed   by 

Y 


322  ELECTRO-PHYSIOLOGY 


artificial  cross -sections,  while  the  upper  surface  (the  "natural 
longitudinal  section  "  of  du  Bois)  corresponds  with  the  natural, 
uninjured  surface  of  the  muscle.  If  unpolarisable  electrodes  are 
so  applied  to  the  muscle -prism  that  the  one  leads  off  from  the 
artificial  cross-section,  the  other  from  the  middle  of  the  natural 
longitudinal  section,  it  will  be  found,  with  a  properly  sensitive 
galvanometer  in  the  circuit,  that  there  is  invariably  a  pronounced 
deflection,  i.e.  a  current,  which  flows  in  the  leading -off  circuit 
from  longitudinal  to  transverse  section,  in  the  muscle  on  the 
contrary  from  cross-section  to  longitudinal  surface. 

Since  any  point  of  the  longitudinal  section,  when  connected 
with  any  point  of  the  transverse  section,  invariably  gives  a 
current  in  the  same  direction,  it  may  be  stated  generally  that  the 
entire  surface  of  the  muscle  cylinder  is  positive,  and  every  cross- 
section  of  the  same  negative  in  potential.  It  soon  appears, 
however,  that  the  distribution  of  potential  is  unequal ;  if  the 
muscle  cylinder  is  conceived  as  divided  in  two  halves,  by  a 
plane  parallel  with  its  ends,  and  passing  through  the  centre,  the 
greatest  positive  potential  at  the  surface  corresponds  with  the 
"  equator,"  i.e.  the  circumference  of  this  section.  Erom  the  equator 
the  positive  potential  on  either  side  declines  unequally,  i.e.  falls 
more  rapidly  towards  the  end-surfaces,  until  at  the  margin  between 
longitudinal  and  transverse  section  it  becomes'  practically  zero. 
Every  line  of  potential,  or  isoelectric  curve,  therefore,  forms  a  circle 
parallel  with  the  equator.  The  negative  potential  always  decreases 
at  the  ends,  on  either  side,  from  centre  to  periphery.  It  is  easy  to 
see  from  this  distribution  of  potential  that  the  magnitude  of  decline 
may  vary  considerably,  according  to  the  position  of  the  electrodes 
of  the  leading -off  circuit,  so  that  the  lines  of  current  can 
fall  into  a  strong,  weak,  or  ineffective  arrangement.  There  will 
obviously  be  no  current  on  leading  off  from  two  points  of  the 
equator,  or  any  isoelectric  curve  parallel  with  it ;  nor  from  points 
of  the  longitudinal  section  symmetrical  with  the  equator,  or 
corresponding  points  of  the  terminal  sections.  On  the  other 
hand,  a  weak  variation  appears  on  leading  off  from  two  points  of 
the  longitudinal  section  asymmetrical  with  the  equator,  or  two 
asymmetrical  points  of  the  section  itself,  or  from  both  artificial 
cross-sections.  Fig.  102  gives  a  schematic  representation  of  all 
these  possible  cases  ;  a,  h,  c,  cl  stand  for  sections  of  the  muscle 
cylinder ;  the  arrows  show  the  direction  of  current  flowing  into 


ELECTROMOTIVE  ACTION  IN  MUSCLE 


323 


the  leading-off  circuit.      There  is  practically  no  current  in  the 
circuit  uniting  symmetrical  points. 

If  the  potential  at  each  point  of  a  longitudinal  section  is 
expressed  by  an  ordinate,  falling  upon  the  longitudinal  section  as 


abscissa,  the  line  which  unites  the  summits  of  the  ordinates  will, 
in  consequence  of  the  rapid  decline  of  potential  towards  the 
end -surfaces,  be  a  curved  line  with  a  sharp  drop  at  either 
extremity.  A  similar  effect  is  produced  at  the  cross -section 
(Fig.  103). 

If  the  regular  muscle  cylinder  is  shortened  by  making  new 
sections,  cylinders  (prisms)  will  result,  which  follow  the  same  law 
of  the  muscle  current ;  the  muscle  can  further  be  split  up  longi- 


FiG.  103. — Distribution  of  potential  in  straight  muscle  cylinder.     (Rosenthal.) 

tudinally,  parallel  with  the  fibres,  so  that,  as  du  Bois  expresses  it, 
an  artificial  longitudinal  section  is  formed  which,  like  the  natural 
surface,  is  positive  to  the  transverse  section.  And  no  doubt  if  it 
were  possible  to  investigate  a  single  j^rimitive  fihre  in  itself,  the 
same  opposition  would  still  obtain  between  longitudinal  section 


324  ELECTRO-PHYSIOLOGY  chap. 

and  transverse  section.  Indeed,  there  is  some  justification  for 
the  further  postulate  of  electromotive  activity  in  the  same  sense 
in  each  fraction  of  a  primitive  fibre.  Thus  du  Bois-Eeymond 
arrived  at  the  conclusion  that  each  muscle-fibre  was  composed  of 
minute  electromotive  particles  ("  molecules  ")  suspended  in  a  con- 
ducting fluid,  and  he  developed  on  this  basis  a  theory  of  the 
electrical  phenomena  in  animal  tissues,  which  long  held  the  field 
undisputed.  It  was  a  necessary  corollary  of  this  view  to  suppose 
— as  seemed  to  be  supported  by  experiment — that  uninjured, 
striated  muscle  with  a  natural  transverse  section  gave  exactly  the 
same  electromotive  reaction  as  that  furnished  with  an  artificial 
cross-section.  By  "  natural  transverse  sections  "  du  Bois-Eey- 
mond understands  the  total  of  the  uninjured  ends  of  muscular 
fibres  still  normally  connected  with  the  tendon.  This  theory  of 
the  electromotive  equivalence  of  artificial  and  natural  cross- 
sections  rests  mainly  upon  the  electromotive  reaction  of  the 
apparently  uninjured  frog's  gastrocnemius,  and  the  complicated 
structure  and  general  application  of  this  muscle  make  it  advisable 
to  examine  more  closely  into  the  much-discussed  "  gastrocnemius 
current."  Leaving  out  for  the  moment  the  fact  that  the  really 
uninjured  muscle  gives  no  electromotive  reaction  {infra),  it  may  be 
assumed  that  the  achilles  tendon  is,  as  in  the  majority  of  cases 
where  no  special  precautions  are  taken,  negative  towards  the 
remaining  surface  of  the  muscle.  Owing  to  the  complex  struc- 
ture, the  distribution  of  surface  potential  will  then  be  far  more 
elaborate  than  in  a  muscle  cylinder  with  regular  parallel  fibres. 
Eosenthal  (2)  gives  a  very  comprehensive  description  of  the 
structure. 

"  Two  plates  of  tendon,  above  and  below,  are  joined  by 
muscle -fibres  running  obliquely  between  them,  so  as  to  form  a 
semiplumiform  muscle.  N'ow  let  the  upper  tendon -plate  be 
folded  in  the  middle,  like  a  sheet  of  paper,  and  the  two  halves 
grown  together.  There  is  thus  an  upper  plate  of  tendon  lying 
inside  the  muscle,  with  muscle -fibres  starting  obliquely  from  it 
on  either  side ;  the  lower  tendon  is,  however,  curved  through 
the  folding  together  of  the  upper,  so  that  the  whole  muscle 
assumes  the  form  of  a  root,  cleft  longitudinally ;  its  smooth 
surface  (which  faces  the  bone  of  the  shank)  consists  entirely  of 
muscle-fibres,  and  exhibits  only  a  fine  longitudinal  streak  as  indi- 
cation of  the  tendon  concealed  within,  while  the  bulging  dorsal 


ELECTROMOTIVE  ACTION  IN  MUSCLE 


325 


aspect  is    covered  in   its  lower  two-thirds  by  tendon-substance, 
continued  below  into  the  tendo  achilles"  (Fig.  104). 

The  gastrocnemius  is  therefore  provided  by  nature  with  an 
oblique    transverse,   and    a    natural   longitudinal    section,    which 


Fig.  104. — -Scheuia  of  Gastrocnemius  structure.    (Du  Bois-Reymond.) 

include  the  whole  of  the  flat,  and  a  small  part  of  the  bulging 
surface.  This  is  in  correspondence  with  the  characteristic  dis- 
tribution of  potential  on  the  surface  of  the  muscle.  If  a  regular 
muscle  cylinder  is  twisted  obliquely  (Fig.  105)  so  that  the 
terminal  cross-sections  run  parallel  with  each  other,  but  obliquely 
with  the  axis,  the  curve  of  greatest  positive  potential  corresponds, 
not  with  the  equally  oblique,  centrally  placed,  elliptical  equator, 
but  with  a  winding  curve  drawn  towards  the  blunt  corners. 
Conversely,  the  negative  potential  is  greater  at  the  sharp,  than  at 


Fig.  105. — Distribution  of  potential  in  oblique  muscle  cylinder.     (Rosentlial.) 


the  blunt,  corners  of  the  cross-section.  When  there  is  no  current 
through  the  regular  muscle  cylinder,  so  that  the  contacts  of  the 
leading-off  circuit  are  equidistant  from  the  geometrical  equator, 
it  is  evident  that  a  current  will  be  obtained,  flowing  in  the  muscle 
from  sharp  to    blunt   edge  (du  Bois'  "  Neigungstrom ").       Such 


326  ELECTRO-PHYSIOLOGY 


currents  are  exhibited  by  the  gastrocnemius  provided  ctb  initio 
with  an  oblique  section.  A  strong  current  is  effectually  obtained 
on  leading  off  from  the  upper  and  lower  ends  of  the  muscle, 
flowing  in  the  muscle  itself  in  an  ascending  direction.  But  cur- 
rents of  greater  or  less  strength  appear  with  almost  any  lead-off, 
since  equipotential  points  are  rare  upon  the  surface. 

If  the  ascending  gastrocnemius  current  is  not  too  weak  it 
may  easily — like  all  longitudinal  currents — be  demonstrated 
with  the  "  physiological  rheoscope  "  (rheoscopic  leg),  and  this  not 
merely  in  the  experiment  of  Galvani  and  Volta  as  "  contraction 
without  metals,"  in  which  the  sciatic  nerve  drops  upon  the  convex 
surface  of  the  muscle,  and  causes  an  external  short-circuiting  of 
the  current  through  the  nerve,  but  also  by  including  the  nerve 
in  a  circuit  of  low  resistance  led  off  from  longitudinal  and  trans- 
verse section.  In  this  way  a  twitch  is  obtained  from  the  leg  on 
closing,  and  subsequently  on  opening,  the  circuit.  While  at  the 
time  of  the  famous  dispute  between  Galvani  and  Volta,  it  was  the 
excitation  of  a  motor  nerve  through  the  muscle  current,  in  the 
form  of  "  contraction  without  metals,"  that  excited  the  greatest 
interest,  since  the  experiment  appeared  to  be  a  direct  proof  of  the 
existence  of  an  electricity  peculiar  to  the  animal  tissues,  the  interest 
in  this  point  subsequently  disappeared  when  it  was  no  longer 
disputed.  On  the  other  hand,  another  attempt  to  demoiistrate 
the  muscle  current  hj  a  physiological  method,  deserves  more 
attention.  If  the  current  of  the  longitudinal  section  suffices  to 
excite  the  nerves  of  a  rheoscopic  leg,  it  is  conceivable  that  the 
muscle  itself  may  be  excited  by  its  own  current,  or  current  from 
another  muscle  (Hering,  4). 

As  early  as  1859  Kiihne  (3)  described  a  characteristic 
reaction  in  the  transversely  divided  frog's  sartorius,  appearing 
when  the  cut  surface  was  dipped  into  various  fluids,  and  ascribed 
by  him  to  chemical  excitation  of  the  exposed  fibres.  If  the 
vertically  dependent,  curarised  muscle  is  brought  into  contact 
with  a  watch-glass  of  0*6  °/„  NaCl,  immediately  after  making 
a  section,  a  twitch  almost  invariably  follows  at  the  moment 
of  contact  between  cut  surface  and  fluid.  The  muscle  is  thus 
jerked  out  of  the  fluid,  but  on  relaxing  it  dips  in  again,  when 
a  second  twitch  follows,  and  so  on.  In  this  manner  a  long 
series  of  rhythmical  contractions  (over  100)  may  be  discharged. 
The  experiment  comes  off  with  a  number  of  other  fluids.     Besides 


IV  ELECTROMOTIVE  ACTION  IX  MUSCLE  327 

different  concentrations  of  NaCl  solution,  Kiihne  found  that 
solutions  of  fixed  alkalies  and  mineral  acids  up  to  O'l  ^ 
were  very  effective,  as  well  as  solutions  of  different  salts,  but  he 
failed  to  detect  a  twitch  when  the  section  was  brought  into  con- 
tact with  distilled  water,  alcohol,  creosote,  concentrated  glycerin, 
and  syrupy  lactic  acid ;  Wundt  and  Schelske  further  noted  that 
concentrated  solutions  of  sublimate  produce  no  twitch  from  the 
transverse  section.  Kiihne  held  that  (siqjra)  all  cases  in  which 
he  observed  twitches,  on  touching  a  fresh  section  with  fluid, 
were  due  to  chemical  excitation  of  the  exposed  fibres.  But  this 
is  a  doubtful  hypothesis  in  view  of  the  fact  that  with  0"5-0'6  °/o 
NaCl  solution,  which  is  well  known  to  be  comparatively  harm- 
less, the  effects  in  question  appear  peculiarly  well  marked  and  per- 
sistent. It  is,  moreover,  remarkable  that  salt  solution  when  applied 
to  the  muscle  section  that  has  been  moistened,  does  not  produce 
any  permanent  excitation,  as  would  be  the  case  if  the  fluid  acted 
as  a  chemical  stimulus.  And  it  may  be  shown  that  the  excitatory 
effect  fails  if  the  solution  is  applied  to  the  transverse  section  only, 
and  hardly,  if  at  all,  to  the  longitudinal  surface  of  the  muscle. 
Hering  (4)  produced  this,  inter  alia,  by  placing  a  small  strip 
of  greased  paper  round  the  cross-section  of  the  muscle,  so  that  its 
lower  margin  coincided  with  the  margin  of  the  section.  A  muscle 
prepared  in  this  way  does  not  twitch  on  bringing  the  transverse 
section  into  contact  with  the  salt  solution,  as  must  inevitably 
occur  if  it  was  a  chemical  excitation.  "  If,  on  the  other  hand,  the 
muscle  is  dipped  into  the  fluid  above  the  strip,  the  twitch 
reappears  again."  Accordingly  if  the  experiment  is  to  succeed 
"  it  is  essential  that  there  should  be  on  the  one  hand  a  connection 
between  the  transverse  section  and  the  lowest  part  of  the  longi- 
tudinal surface,  while  on  the  other  this  conductor  must  not  have 
too  great  a  resistance,  i.e.  the  quantity  of  NaCl  solution  which 
produces  it  must  not  be  insufticient."  If  then — as  can  hardly  be 
doubted  from  the  above — this  is  an  electrical  excitation  of  the 
muscle,  by  sudden  short-circuiting  of  its  own  current  within  the 
wall  of  fluid  that  rises  at  the  moment  of  contact,  from  transverse 
to  longitudinal  section,  it  is  easy  to  understand  that  all  non- 
conducting, or  ill-conducting  fluids,  as  we  learn  from  experiment, 
are  ineffective,  even  if  they  have  a  demonstrable  chemical  action 
on  the  substance  of  muscle  (sublimate,  alcohol,  water).  Indeed, 
as    Hering   pointed   out,   the   mere   reaction    of   the    muscle    on 


328  ELECTRO-PHYSIOLOGY 


touching  its  cross-section  with  a  fluid  is  a  tolerably  sure  indication 
as  to  whether  such  a  fluid  is  a  good  or  bad  conductor.  Upon 
this  assumption  we  may  explain  other  easily  verified  experiments, 
which  to  some  degree  are  mere  modifications  of  the  fundamental 
experiment  quoted.  If  a  drop  of  salt  solution  is  allowed  to  fall 
upon  a  cut  at  right  angles  to  the  direction  of  the  fibres  in  a 
muscle,  the  cut  ends  usually  twitch,  and  the  wound  gapes  open. 
Again  a  twitch  can  be  provoked  from  the  transversely  cut  sartorius 
if  the  longitudinal  and  transverse  sections  are  connected  by  a  moist 
conductor  {e.g.  strip  of  liver,  dead  muscle,  etc.)  The  preparation 
can  also  be  laid  upon  unpolarisable  zinc  trough  electrodes  with 
mercury  closure,  leading  ofi^  from  the  fresh  transverse  section 
and  a  point  of  the  longitudinal  section  adjacent  to  it.  Again,  if 
the  cross-section  of  a  freely  dependent  sartorius  is  brought  into 
contact  with  the  longitudinal  surface  by  bending  the  end  with  a 
glass  rod,  the  muscle  will  twitch  from  the  sudden  closure  of  its  own 
current.  Finally,  Hering  succeeded  in  producing  a  twitch  in  an 
uninjured,  by  current  from  an  injured,  muscle.  To  this  end  the  un- 
injured sartorius  was  fixed  by  the  bones  so  as  to  hang  down  in  a  slack 
curve.  The  second  vertical  muscle  was  then  brought  into  contact 
with  it,  the  cross-section  being  applied  to  the  surface  of  the  first 
nmscle.  "  When  both  muscles  are  very  excitable  they  may  both 
twitch ;  for  as,  on  contact  with  the  cross-section,  it  is  very  likely 
that  part  of  the  longitudinal  surface  also  will  be  in  contact  with 
the  uninjured  muscle,  closure  of  current  in  the  injured  muscle 
is  efiected  by  the  uninjured,  and  both  are  simultaneously  excited." 
This  always  occurs,  indeed,  if  the  cut  end  is  bent  over.  In  all 
these  experiments  short-circuiting  of  the  muscle  current  is  efiected 
by  moist  conductors.  Metals  indeed  are  of  very  little  use  on 
account  of  their  extraordinarily  rapid  polarisation,  though  at  first 
sight  the  contrary  might  be  expected.  Hering,  like  Kiihne  (5), 
found  little  or  no  twitch,  when  contact  was  formed  at  the  fresh 
cross-section  of  a  curarised  sartorius  by  a  platinum  plate,  while 
a  wire  of  the  same  metal,  connected  with  a  mercury  key,  effected 
contact  at  different  points  of  the  conducting  surface. 

The  fact  that  current  from  the  longitudinal  muscle  section 
may  under  certain  conditions  excite  not  only  the  nerve  of  a 
rheoscopic  leg,  but  also  the  injured  muscle  itself,  or  even  one 
that  is  uninjured,  gives  a  ^:*?"'ioW  reason  to  suppose  that  the 
same  factor  plays   a  part  in   all  electrical  excitation  of  injured. 


IV  ..  <■  ELECTROMOTIVE  ACTIOX  IN  MUSCLE  329 

i.e.  electromotive,  muscle,  and  it  is  the  more  essential  to  bear  in 
mind  these  phenomena  of  interference  hehveen  the  artificial  and 
the  natural  current,  since  they  involve  facts  which  have  led  to 
important  theoretical  conclusions. 

We  have  already  cited,  as  a  cogent  proof  of  the  validity 
of  the  lav7  of  polar  excitation,  the  characteristic  response  of  a 
muscle  with  parallel  fibres,  injured  at  one  end  only,  to  longi- 
tudinal passage  of  current ;  as  seen,  e.g.,  in  the  fact  that  the 
excitatory  effect  of  closure  or  opening  of  a  current  is  invariably 
diminished  or  abolished,  when  it  leaves  or  enters  by  the  demarca- 
tion surface.  Since  in  the  former  case  the  direction  of  that 
fraction  of  the  muscle  current  which  branches  into  the  exciting 
circuit  is  always  opposed  in  direction  to  the  battery  current, 
the  latter  is  necessarily  weakened  by  the  former,  and  the 
question  arises  whether  this  in  itself  would  not  be  sufficient  to 
account  for  the  diminished  excitation  at  closure  of  the  circuit. 
Obviously  in  this  case,  if  the  muscles  are  introduced  into  the 
same  circuit,  one  behind  the  other,  one  of  them  being  injured  at 
one  end,  the  closure  of  the  current  would  affect  both  muscles 
equally,  i.e.  the  make  excitation  with  admortal  direction  of  current 
would  be  abolished  or  lessened,  not  merely  in  the  muscle  with  an 
artificial  cross-section,  but  in  the  normal  preparation  also.  Yet 
this  is  not  the  case,  and  the  theory  is  no  less  definitely  refuted 
by  the  fact  that  the  death  of  the  fibres  at  hoth  ends  of  a  muscle 
with  parallel  fibres,  produces  the  same  depression,  or  abolition, 
of  excitability  towards  the  closure  of  ascending  as  of  descending- 
currents.  On  the  other  hand,  it  appears  as  if  the  augmented 
effect  which  is  often  to  be  seen  at  closure  of  weak  "  abter- 
minal "  battery  currents  after  injury  to  one  end  of  the  sar- 
torius,  is  essentially  caused  by  the  deriving  current  from  the 
muscle  superadded  in  this  case,  algebraically,  to  the  exciting 
current. 

Under  certain  conditions,  to  be  discussed  below,  a  spurious 
break  twitch  appears  in  consequence  of  interference  between  the 
demarcation  current  and  an  artificial  excitation  current,  which 
might  easily  be  taken  for  the  effect  of  a  real  break  excitation, 
and  is  in  fact  frequently  confused  with  it.  Given  a  leading-in 
circuit  of  comparatively  low  resistance,  so  connected  with  a 
curarised  sartorius  provided  at  the  pelvic  end  with  an  artificial 
cross -section,  that  the  unpolarisable  contacts  are  applied,  on  the 


330  ELECTRO-PHYSIOLOGY 


one  side  to  the  cross-section  (or  bones  of  the  pelvis  leading  off' 
from  it),  on  the  other  side  to  the  tibial  end  of  the  tendon  (or 
tibia  itself)  ;  then  at  the  moment  of  closing  the  circuit,  which 
has  been  broken  at  any  point,  the  longitudinal  current  will 
equalise  itself,  and  will  presumably,  on  leaving  the  normal 
muscular  substance  at  the  small  end  of  the  muscle,  discharge  a 
make  twitch,  if  the  intensity  of  the  shunt  current  is  sufficient, 
the  resistance  in  the  circuit  being  as  low  as  possible — conditions 
which  are  scarcely  afforded  in  the  case  before  us.  But  if  we 
suppose  for  a  moment  that  we  are  really  dealing  in  this  case 
with  discharge  of  a  make  twitch  of  the  muscle  through  short- 
circuiting  of  its  own  current,  a  twitch  that  was  referable  to 
this  cause  would  also  be  produced  if  the  fraction  of  the  muscle 
current  shunted  off  was  compensated,  or  even  over-compensated, 
by  a  galvanic  current  sent  through  the  intrapolar  tract,  i.e.  the 
entire  muscle,  in  an  ascending  direction — finding  closure  again 
suddenly  at  the  instant  the  battery  current  is  broken.  In  the 
case  in  which  compensation  is  complete,  and  unavoidable  secondary 
effects  of  the  compensating  current  negligible,  the  excitation 
effect  will  be  as  great  on  opening  the  galvanic  current  as  on 
the  previous  closure  of  the  circuit.  The  experiment  is  sure  to  be 
successful,  if  the  resistance  in  the  leading-off  circuit  is  reduced 
as  much  as  possible  by  shortening  the  intrapolar  tract  of  the 
muscle  (6). 

It  is  often  sufficient  to  use  the  lower  half  of  the  sartorius 
only,  by  killing  a  segment  in  the  middle  of  the  muscle  with 
heat  (artificial  thermic  section),  fastening  this  point  with  small 
needles  to  a  cork  plate,  and  leaving  the  lower  third  of  the  muscle 
free,  weighted  only  by  the  dependent  tibia.  Two  unpolarisable 
electrodes,  one  of  which  is  placed  upon  the  upper  margin  of  the 
tract  destroyed,  while  the  other  (near  the  tibia)  dips  into  a  vessel 
with  concentrated  salt  solution,  serve  on  the  one  hand  to  lead  off 
the  muscle  current,  and  on  the  other  to  lead  in  the  com- 
pensating battery  current  from  a  Daniell  cell.  In  order  to 
graduate  the  intensity  of  the  latter,  a  rheochord  is  introduced 
into  the  circuit,  which  serves  as  a  deriving  circuit  to  the 
muscle.  Provision  should  be  made  for  opening  the  circuit  at 
two  different  points,  since  the  object  is  to  investigate  the 
difference  in  excitation  effect  on  breaking  the  main  current  with 
simultaneous    sliort- circuiting   of    the    muscle    current,  and   on 


IV  ,  ..        ELECTROMOTIVE  ACTIOX  IX  MUSCLE  331 

simply  cutting  out  the  former.  For  this  purpose  two  mercury 
keys  are  introduced  into  the  circuit,  one  between  the  cell  and  the 
rheochord,  the  other  between  the  latter  and  the  nniscle.  The 
former  is  denoted  below  as  the  key  in  the  principal  circuit, 
the  latter  as  key  in  the  deriving  circuit.  If  the  key  of  this 
deriving  circuit  is  closed  immediately  after  the  thermic  section  has 
been  effected,  the  key  of  the  primary  circuit  remaining  open,  a 
perfectly  visible,  though  usually  weak,  closure  twitch  is  seen 
under  favourable  conditions  in  very  excitable  preparations.  The 
results  are  more  certain  if  the  unpolarisable  electrodes  are  placed 
near  together,  in  direct  lateral  contact  with  two  points  of  the 
surface  of  the  muscle,  whereby  the  resistance  in  the  circuit  can  be 
suitably  reduced.  If  the  upper  half  of  the  uninjured  sartorius 
is  stretched  on  a  cork  plate,  and  one  electrode  placed  at  the 
pelvic  end,  the  other  at  a  slightly  lower  point  of  the  longitudinal 
surface,  then  on  leading  a  weak  or  medium  current,  descending 
or  ascending,  through  the  muscle,  a  twitch  occurs  at  every 
closure,  while  on  opening  the  circuit  by  the  principal,  or  shunt 
key,  no  trace  of  change  of  form  in  the  muscle  is  apparent. 
The  result  of  the  experiment  is  very  different  when  an  artificial 
(thermic)  section  has  previously  been  made  at  the  pelvic  end 
of  the  muscle ;  if  the  negative  electrode  is  now  in  contact  with 
the  heat-rigored  end  of  the  muscle,  while  the  positive  electrode 
is  applied  to  the  nearest  point  of  the  uninjured  surface,  there  is, 
with  rare  exceptions,  in  excitable  preparations,  immediately  after 
the  injury,  a  distinct  twitch,  the  index  of  excitation  in  the  freely- 
depending  half  of  the  muscle,  as  soon  as  the  deriving  circuit  is 
closed — the  principal  circuit  remaining  open.  It  is  obvious 
from  the  conditions  of  the  experiment  that  this  also  is  an 
excitation  resulting  from  the  passage  of  the  muscle  current 
through  the  shunt  current.  Whether  this  happens  or  not,  there 
is  invariably,  under  these  experimental  conditions,  a  pronounced 
shortening  of  the  muscle  when  a  weak  battery  current  opposed 
in  direction  to  the  muscle  current  (i.e.  in  this  case  ascending)  is 
made  for  a  short  time  and  broken  in  the  principal  circuit.  Since 
the  physiological  kathode  is  at  the  seat  of  injury,  the  make 
excitation  either  fails  altogether,  or  is  very  insignificant.  This 
result,  however  (given  a  sufficient  distance  of  the  leading-off,  or 
leading-in,  electrodes),  appears  at  the  opening  of  the  principal 
circuit  only,  wdiile  there  is  no    sign   of  mechanical    change    on 


•332  ELECTRO-PHYSIOLOGY 


opening  the  deriving  circuit.  A  maximum  difference  of  electrical 
potential  in  the  points  of  the  muscle,  from  which  the  electrodes 
lead  off,  as  well  as  lead  in,  is  the  only  indispensable  condition. 
In  view  of  the  preceding  discussion,  there  can  be  no  doubt 
that  the  striking  difference  of  effect  on  breaking  the  circuit  at 
two  different  points,  is  solely  due  to  the  fact  that  the  demarca- 
tion current  in  the  one  case  finds  an  external  circuit  of  com- 
paratively low  resistance  on  opening  the  balttery  current,  which 
is  wanting  in  the  other  case.  The  twitch,  though  coincident 
in  time  with  the  moment  of  breaking  the  circuit,  cannot 
be  regarded  as  a  true  opening  twitch  due  to  internal  reaction 
of  the  muscle,  but  is  much  rather  a  closure  twitch,  discharged 
by  external  short-circuiting  of  the  muscle  current  (Bieder- 
mann,  6). 

If  the  distance  between  the  two  electrodes  is  very  small, 
there  will,  as  a  rule,  even  with  minimal  currents,  be  hardly  any 
perceptible  difference  in  the  magnitude  of  the  break  twitches, 
whether  the  battery  circuit  or  the  muscle  circuit  is  opened. 
Intermediate  electrode  points  may  be  found,  in  which  there  is  a 
certain  difference  in  the  magnitude  of  twitch,  according  as  it  is 
discharged  at  break  of  the  principal,  or  deriving,  circuit,  since 
in  the  latter  case  it  decreases  in  proportion  as  the  point  of 
entrance  of  the  atterminal  battery  current  recedes  from  the  limit 
of  the  thermic  section,  the  kathodic  contact  at  the  cross-section 
remaining  unaltered.  This  is  easily  explained  in  view  of  the 
pronounced  internal  short-circuiting  of  the  muscle  current  that 
always  occurs  in  the  immediate  vicinity  of  the  electromotive 
surface.  For  if  countless  lines  of  current  pass  out  at  the  surface, 
in  parts  that  are  still  excitable,  near  each  transverse  section  of 
each  single  primitive  fibre,  and  thus  of  the  entire  muscle,  a 
battery  current  entering  at  this  region  of  internal  short-circuiting 
must  i'pso  facto  compensate  a  portion  of  these  lines  of  current, 
some  completely,  some  imperfectly,  while  others  again  may  be 
over-compensated.  This,  however,  implies  that  those  spots  more 
or  less  entirely  lose  their  character  as  kathodic  points  of  the 
muscle  current,  or  even  become  anodic  points  of  the  battery 
current.  If  the  latter  is  opened  again,  the  former  condition 
is  instantly  recovered ;  the  points  once  more  become  kathodic 
points  of  the  muscle  current,  and  are  excited  by  it.  The 
battery  current  therefore  abolishes  in  part  the  internal  closure 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  333 

of  the  muscle  current,  the  sudden  restoration  of  which,  at  break 
of  the  battery  current,  produces  a  make  contraction. 

It  is  indeed  a  matter  of  indifference  whether  the  break  of  the 
galvanic  current  occurs  in  the  muscle  or  battery  circuit ;  in  the 
latter  case  it  must  be  taken  into  consideration  that  the  branch 
of  the  muscle  current,  which  is  closed  by  the  rheochord,  and 
compensated,  or  over-compensated,  during  the  passage  of  the 
galvanic  current,  finds  its  closure  at  the  moment  the  latter  is 
broken,  and  hence  induces  the  "  spurious  break  twitch."  The 
theoretical  differences  in  magnitude  of  twitch  in  either  case  are 
not,  however,  perceptible,  because  the  contractions  are  very 
marked  in  both  cases. 

Since  the  last-named  effects  of  excitation  are  of  importance  in 
regard  to  certain  facts  respecting  electrical  excitation  of  nerve,  to 
be  described  below,  we  must  consider  them  a  little  more  in  detail. 
If  a  loop  of  moist  thread  is  laid  round  the  muscle — stretched, 
to  obtain  a  graphic  record  of  its  twitches,  in  Hering's  double 
myograph — so  that  the  current  enters  anywhere  in  its  continuity, 
in  the  close  vicinity  of  an  artificial  section  produced  by  crushing, 
while  it  leaves  it  again  at  the  pelvic  bone,  pronounced  break 
contractions,  which  are  almost  entirely  independent  of  the  length 
of  closure,  may  be  seen  directly  a  weak  current  is  sent  in,  without 
regard  to  the  point  at  which  the  circuit  is  opened.  If,  while  the 
kathode  remains  in  situ  at  the  uninjured  pelvic  end  of  the 
sartorius,  the  physiological  continuity  of  the  muscle  is  interrupted 
somewhere  near  the  middle  by  crushing  with  forceps,  the  thread 
being  applied  now  to  one  side,  and  now  to  the  other,  of  the  seat 
of  injury,  but  always  close  to  its  margin,  break  contractions  may 
be  seen  in  both  cases  at  equal  current  intensity,  in  one  of  the 
halves  divided  by  the  injury,  the  contraction  being  always  in 
that  half  where  current  enters  at  the  artificial  section.  If 
the  electrode  by  which  current  enters  is  removed  ever  so  little 
from  the  point  of  injury,  the  effects  of  excitation  being  tested  at 
each  new  position,  it  may  be  seen  that  the  "  spurious  break 
twitches  "  as  a  rule  become  weaker,  even  at  points  of  the  normal 
longitudinal  surface  that  are  no  more  than  2  mm.  from  the  part 
injured,  and  disappear  altogether  as  soon  as  the  thread  is  moved 
still  further,  provided  closure  is  effected  by  the  key  of  the  deriv- 
ing circuit. 

If  we  are  justified  in  saying  that  the  only  fact  of  importance 


334  ELECTRO-PHYSIOLOGY 


in  the  discharge  of  spurious  break  twitches  by  internal  shunting 
of  the  demarcation  current,  is  that  the  kathodjc  points  of  fibres 
in  immediate  juxtaposition  with  the  electromotive  surface,  by 
which  current  leaves  the  muscle,  become  temporarily  the  points  of 
entrance  of  an  adequate  galvanic  current  (in  which  case  there  will 
only  be  partial  compensation  of  the  demarcation  current),  it  might 
be  expected  that  spurious  break  twitches  would  appear,  not  only 
— as  in  the  case  described  above — on  applying  "  atterminal " 
battery  currents,  but  also  when,  on  "abterminal"  passage  of  current 
through  the  entire  muscle  or  a  portion  of  the  same,  the  entry  of 
the  current  occurs  at  the  limit  of  an  artificial  cross-section  in 
the  region  where  the  muscle  current  leaves  it.  It  is  in  fact 
sufficient,  for  the  discharge  of  spurious  break  twitches  of  great 
vigour,  to  make  an  artificial  section  at  the  pelvic  end  of  a 
sartorius,  followed  immediately  by  a  weak  descending  galvanic 
current  through  the  entire  muscle,  entering  laterally  close  under 
the  margin  of  dead  and  living  substance  by  means  of  a  thread 
electrode. 

If  further,  with  abterminal  direction  of  current,  the  dead  ends 
of  fibres  are  conceived  as  connected  by  any  kind  of  conductor 
with  the  zone  of  normal  longitudinal  muscle -surface  imping- 
ing on  the  border,  we  might  expect  spurious  opening  effects  of 
excitation  in  this  case  also.  Such,  e.g.,  do  appear  when  one  end 
of  the  muscle  is  crushed  with  small  forceps ;  the  bulging  and 
curving  of  the  longitudinal  surface  of  the  fibres  then  give  repeated 
opportunities  to  both  muscle  current  and  battery  current  to  enter 
and  leave  at  points  in  the  uninjured  surface  of  the  muscle,  and 
thus  to  discharge  effective  make,  or  spurious  break,  excitations. 
If,  after  ascertaining  that  an  ascending  current  of  medium  intensity 
discharges  no  perceptible  break  excitation  in  a  sartorius  stretched 
in  the  double  myograph,  the  muscle  is  crushed,  as  indicated,  close 
to  the  lower  end  of  the  tendon,  opening  twitches  will  appear 
almost  uniformly — direction,  intensity,  and  duration  of  closure  of 
the  excitino-  current  remaining  constant — and  must,  according  to 
the  above,  be  regarded  as  spurious  (Biedermann,  6  ;  Engel- 
mann,  7). 

From  this  digression  we  may  return  to  the  consideration  of 
the  "  current  of  rest "  in  muscle,  its  properties  and  its  origin. 
Since,  provided  the  galvanometer  swings  are  not  excessive,  the 
deflections  are  known  to  be  proportional  to  the  intensity  of  the 


ELECTROMOTIVE  ACTION  IN  MUSCLE 


335 


current,  it  is  of  course  easy  to  measure  the  intensity  of  the 
muscle  current ;  yet,  in  view  of  the  great  and  very  variable 
resistance  of  vegetable  and  animal  tissues,  such  measurements  are 
on  the  whole  of  little  value.  Much  greater  importance  attaches 
on  the  other  hand  to  exact  measurements  of  cleetromotive  force. 
If  two  points  of  different  potential  are  connected  by  a  leading- 
off  circuit  to  a  conductor  which  is  the  seat  of  electromotive  force, 
a  branch  of  the  current  will  flow  through  these,  of  intensity 
directly  proportional  with  the  E.M.F.  which  may  be  conceived  as 
acting  at  the  points  of  junction.  The  magnitude  of  the  latter 
may  thus  be  measured  from  the  difference  in  potential  between 
two  points  led  off,  and  where 
it  is  possible  to  determine  this 
exactly,  it  is  also  possible  to 
determine  the  magnitude  of  the 
electromotive  force.  And  the 
E.M.F.  of  the  longitudinal  current 
could  be  ascertained  simply  by 
measuring  the  P.D.  between 
natural  longitudinal  surface  and 
artificial  cross-section.  The  dif- 
ference of  potential  between  two  " 
points  is  easy  to  determine  ex- 
perimentally, by  a  method  in- 
vented by  Poggendorff,  and  essen- 
tially improved  by  du  Bois- 
Eeymond  (8). 

The  principle  of  the  method  is  to  replace  the  magnet  from 
its  deflected  position  to  its  original  position  of  rest,  by  means  of  a 
fraction  of  the  current  of  a  standard  cell,  opposing  and  cancel- 
ling the  original  current.  The  known  variable  P.D.  is  thus 
a  measure  for  the  magnitude  of  the  unknown  difference  to  be 
determined.  Such  a  "  compensating "  current  can  easily  be 
derived  from  a  measuring  circuit  by  means  of  a  rheochord,  termed 
in  this  case  a  "  compensator."  If  a  constant  current  {K)  is  led 
through  a  straight  or  circular  wire  (Fig.  106  a,  h),  a  definite 
"  electrical  fall "  occurs  in  the  circuit,  since  there  are  diiferences 
of  potential  at  different  points.  JSTow,  if  the  longitudinal  section 
of  a  muscle  (31),  lying  upon  unpolarisable  electrodes,  is  connected 
by  means  of  a  reverser  (C)  with  the  end  (a)  of  the  compensator 


Fig.  106. — Measurement  of  E.M.F.  by  com- 
pensation.    (Du  Bois-Eeymond.) 


336 


ELECTRO-PHYSIOLOGY 


wire,  while  the  point  led  oft'  on  the  longitudinal  section  is  con- 
nected with  a  metal  slider  (c)  leading  to  the  wire  of  the 
rheochord,  the  galvanometer  {B)  will  be  affected  on  the  one 
hand  by  the  difference  of  potential  between  the  rheochord  points 
a  and  c,  on  the  other  by  that  between  the  transverse  and  longi- 
tudinal surfaces  of  the  muscle.  It  is  easy  at  any  moment  by 
moving  the  slider  (c)  to  compensate  the  deflection  produced  by 
the  muscle  current.  The  P.D.  between  longitudinal  and  trans- 
verse section  of  the  muscle  will  then  obviously  be  the  P.D. 
between  the  points  a  and  c  of  the  rheochord  wire.      And  in  the 


Fig.  107((. — Round  Compensator.    (Du  Bois-Reymond.) 

latter  each  millimeter  corresponds  with  a  given  fraction  of  the 
E.M.F.  of  a  Daniell  cell. 

In  order  to  carry  out  these  measurements  quickly  and  con- 
veniently, du  Bois-Eeymond  constructed  the  "  round  compensator," 
in  which  the  rheochord  wire  a,  h  is  attached  to  a  circular  disc  of 
ebonite.  Its  terminals  are  connected  with  screws  I.  and  11. ;  from 
I.  a  wire  also  goes  to  IV.,  III.  being  connected  with  the  metal 
pulley  (7^),  which  slides  upon  the  rheochord  wire,  so  that  a 
given  length  of  it  can  be  included  by  moving  the  slider  (Fig. 
107  a,  h). 

By  this  method  du  Bois-Eeymond  took  numerous  measure- 
ments of  the  electromotive  force  between  longitudinal  and 
transverse  sections  of  striated  frog's  muscle.  The  average  was 
0"035  — 0*075     Dan.      According     to     Matteucci,     the     muscle- 


ELECTROMOTIVE  ACTION  IN  MUSCLE 


337 


current  is  stronger  in  proportion  as  the  animal  is  higher  in  the 
scale,  but  it  is  difficult  to  get  exact  measurements  of  E.M.F. 
in  warm-blooded  muscles,  on  account  of  the  rapid  death  of  the 
tissue.  That  the  muscle  current  is  essential  to  the  preservation 
of  normal  vital  activities  in  the  muscle  appears  directly  from  the 
fact  that  dead  muscle  has  no  electromotive  action,  or  at  most 
exhibits  excessively  irregular  and  weak  reactions.  Moreover,  the 
E.M.F.  of  the  excised  muscle, 
provided  with  a  cross-section, 
undergoes,  as  du  Bois  pointed 
out,  a  slow  decline ;  the  pro- 
cess of  death,  creeping  slowly 
from  the  cut  surface,  gradually 
involves  all  the  injured  fibres 
of  a  muscle,  so  that  they  be- 
come rigored  and  incapable  of 
electromotive  action.  Accord- 
ingly, the  limit  between  dead 
fibres  (confined  at  first  to  the 
cut  surface)  and  the  living  part 
of  the  contractile  substance 
("  the  demarcation  surface ") 
encroaches  inwards  in  the 
course  of  the  rigor. 

We  have  frequently  used 
the  term  "artificial  section," 
even  when  there  was  no  real 
cut  surface,  but  only  a  de- 
marcation surface  as  above. 
As  a  matter  of  fact  each 
dead  bit  of  muscle -fibre  be- 
haves as  an  indifferent  tag  (comparable  with  the  tendon 
substance),  which  leads  off  from  the  artificial  cross  -  section, 
i.e.  limit  between  dead  and  living  fibres.  In  this  sense, 
therefore,  it  is  quite  legitimate  to  speak  of  a  mechanical, 
thermic,  or  chemical  section.  As  a  general  rule,  moreover,  the 
strength  of  the  electromotive  action  is  independent  of  the  kind  of 
death,  or  destruction,  of  a  tract  of  fibres,  so  long  as  the  process 
is  actually  accomplished. 

If  these   experiments   prove  beyond  doubt   that   the  muscle 

z 


338  ELECTRO-PHYSIOLOGY 


current  is  a  property  of  living  tissues,  it  would  still  only  appeal 
to  us  as  a  vital  phenomenon  of  the  first  interest  if  it  could  be 
proved  that  du  Bois-Eeymond's  law  of  the  equivalence  of  natural 
and  artificial  sections  was  universally  valid,  i.e.  that  a  P.D. 
between  the  tendon  end  and  remaining  surface  of  the  muscle, 
corresponding  with  the  muscle  current,  is  demonstrable  in  all 
cases  ;  in  other  words,  if  the  "  ijre-existence  "  of  the  muscle  current 
in  intact  living  animals  were  a  proved  conclusion.  But  this,  as 
we  shall  see,  is  by  no  means  the  case ;  on  the  contrary,  the  result 
of  the  innumerable  experiments  of  a  later  date  has  been  more  and 
more  in  favour  of  the  view  upheld  by  Hermann,  to  the  effect 
that  the  muscle  current  is  not  pre -existent,  but  is  an  artificial 
effect  of  the  preparation.  Matteucci  long  ago  maintained  that 
there  was  no  trace  of  a  muscle  current  in  the  uninjured  living 
animal.  According  to  him  the  current  arises  from  the  leading- 
off  contacts.  Du  Bois-Eeymond,  who  {supra)  adopted  the  theory 
of  a  constant  difference  in  potential  between  the  achilles  tendon 
(natural  section)  and  uninjured  surface  of  the  muscle,  chiefly  on 
account  of  his  first  experiments  with  the  frog's  gastrocnemius, 
was  subsequently  obliged  to  modify  his  opinion.  The  starting- 
point  of  these  last  investigations  of  du  Bois-Eeymond  was  a 
series  of  observations  on  the  effect  of  cold  on  the  nmscle  current, 
which,  as  Matteucci  had  pointed  out,  produces  a  marked  diminu- 
tion. Du  Bois-Eeymond  upon  the  whole  confirmed  Matteucci's 
conclusions  as  to  decreased  action  in  the  muscles  of  cooled  frogs. 
Gastrocnemii  (which,  on  leading  off  from  tendon  and  natural 
longitudinal  section,  invariably  gave,  according  to  du  Bois- 
Eeymond's  original  theory,  a  vigorous  normal  current)  exhibited 
negative  or  reversed  effects  in  the  sense  of  a  descending  muscle 
current,  while  directly  an  artificial  cross-section  was  provided 
they  yielded  an  ascending  current.  Du  Bois-Eeymond  designated 
the  state  of  muscle  induced,  as  he  thought,  by  cold,  the  "parelectro- 
nomic "  state  {'jrapavo/iio'i  =  against  the  law),  because  it  gives  no 
electromotive  response,  or  even  reacts  in  the  opposite  direction. 
The  fact  that  these  parelectronomic  muscles  resume  their  "normal" 
activity  from  the  moment  they  are  laid  upon  pads  of  salt  clay 
coated  with  an  albuminous  membrane,  is  due,  however,  less  to  warm- 
ing than  to  the  slow  chemical  alteration  (corrosion)  of  the  tendon, 
which  is  in  contact  with  the  concentrated  salt  solution  of  the  lead- 
ing-off  electrodes  and  the  albumen  of  the  membrane.     These  fluids 


IV  ELECTROMOTIVE  ACTION  IX  MUSCLE  339 

gradually  induce  the  same  effect  that  is  suddenly  brought  about 
when  a  mechanical  or  thermic  section  is  applied  by  any  method. 
Hermann  (9)  showed  later,  by  conclusive  experiments,  that 
the  E.M.F.  of  excised  muscles  does  sink  considerably  through 
cooling,  and  rises  again  on  increasing  the  temperature ;  according 
to  Hermann  the  variation  may  rise  to  22  ^  within  the  range 
of  vital  temperature,  but  is  probably  still  greater,  since,  in 
the  methods  used,  the  deeper  layers  may  not  be  affected  in  the 
same  degree  as  the  more  superficial. 

If  in  preparing,  as  well  as  in  leading  off  from  the  muscle, 
care  is  taken  to  avoid  all  possible  injury  (especially  at  the  tendon 
end),  the  electromotive  effect  is  either  negative,  or  the  P.D.  between 
surface  and  natural  section  is  so  negligible  that  it  might  legiti- 
mately be  ascribed  to  inevitable  disturbances  from  exposure. 
Moistening  the  natural  section  with  fluids  which  do  not  attack 
the  muscle-substance  chemically,  e.g.  physiological  NaCl  solution, 
gives  no  perceptible  development  of  current.  Later  on  in  du 
Bois-Eeymond's  investigations,  it  appeared  that  the  supposed 
effect  of  cooling  is  not  so  important  in  the  development  of 
parelectronomy,  but  that  all  muscles  are,  rather,  permanently  at  a 
more  or  less  pronounced  grade  of  the  parelectronomic  condition. 
This  state  is  not  therefore  abnormal  and  an  effect  of  cooling,  but 
is  perfectly  normal  and  regular.  As  Hermann  remarks,  the  term 
"  parelectronomic  "  might  with  more  justice  be  applied  to  the  state 
in  which  current  is  fully  developed  between  end  of  tendon  and 
muscle,  than  to  that  which  du  Bois-Eeymond  designates  by  it. 

Du  Bois-Eeymond's  explanation  of  the  parelectronomic  state 
will  be  discussed  below.  Here  it  can  only  be  said  that  he 
attributes  the  failure,  or  absence,  of  current  between  surface 
and  natural  section  to  the  presence  of  a  thin  layer  of  specific 
muscle-substance  at  the  natural  section,  which  by  its  contrary 
action  partly  compensates,  or  even  over-compensates  {i.e.  abolishes), 
the  normal  electromotive  action  of  the  remaining  mass  of  the 
muscle. 

The  production  of  current  when  the  natural  cross-section  is 
moistened  with  concentrated  JSTaCl  solution,  acids,  or  alkalies, 
or  is  cut  or  heated,  must  accordingly  be  referred  to  the  chemical, 
thermic,  or  mechanical  disturbance  of  this  thin  sheet,  called  by 
du  Bois-Eeymond  the  parelectronomic  layer.  This  theory  of  a 
parelectronomic    condition    at    various    stages    of    development 


340  ELECTRO- PHYSIOLOGY  chap. 

affords  a  simple  explanation  of  the  vigorous,  normal  current  of 
the  apparently"  uninjured  gastrocnemius,  as  also  of  the  irregular 
effects  which  may  he  produced  on  leading  off  from  tendon  and 
natural  longitudinal  section  of  the  different  thigh  muscles.  But 
it  is  evident  that,  under  the  given  conditions,  the  state  of  no 
■current  must  be  regarded  as  normal.  If  it  could  be  proved 
that  all  muscles  in  the  perfectly  uninjured  state  are  invariably, 
and  under  all  conditions,  currentless,  the  hypothesis  of  a  special 
layer  working  in  a  contrary  direction  at  the  natural  section  would 
obviously  be  superfluous.  The  entire  controversy  as  to  the  pre- 
existence  of  the  muscle  current  turns,  therefore,  as  Hermann  said, 
upon  whether  it  can  be  demonstrated  before  the  animal  is  skinned, 
on  the  muscle  in  situ,  with  normal  circulation.  This  might  seem 
comparatively  easy  on  the  frog,  since  its  moist,  thin  skin  lies 
loosely  on  the  muscles,  and  forms  a  relatively  effective  sheath. 
And  it  is  in  fact  the  most  favourable  object  for  the  experiment. 
Du  Bois-Eeymond  devoted  much  time  and  trouble  to  the  in- 
vestigation of  the  muscle  current  in  the  living,  uninjured  frog 
with  intact  skin,  and  concluded,  finally,  that  normal  differences 
of  potential  did  exist  in  the  sense  indicated.  Nevertheless,  this 
also  appeared  later  to  be  an  interpretation  against  which  serious 
objections  can  be  urged.  In  leading  off  from  frogs,  and  frogs' 
limbs,  with  intact  skin,  du  Bois-Eeymond  again  employed 
trough  electrodes,  filled  with  concentrated  NaCl,  and  covered 
with  an  "  albumen  membrane."  It  was  soon  found  that  the 
contact  first  applied  was  always  positive  to  the  second  contact,  so 
that  after  some  time  a  current  of  low  E.M.F.  appeared,  in  the 
direction  of  the  longitudinal  current  in  a  skinned  frog.  The  first 
effect  depends,  as  du  Bois  found,  upon  an  electromotive  force  in 
the  skin  of  the  frog  itself.  It  is  here  sufficient  to  state  that  the 
E.M.F.  of  the  skin  is  vertical  to  its  surface,  current  being 
directed-  from  without  inwards  (of  course  reversed  in  the  galvano- 
meter circuit).  Now  since  these  strong  natural  effects  are  easily 
disturbed  by  moistening  the  outer  surface  of  the  skin  with 
corrosive  fluids,  there  must  always  be  a  current  in  the  above 
sense  when  the  skin  is  brought  into  unequal  contact  with  the 
leading-off  electrodes,  since  these  are  not  perfectly  indifferent,  i.e. 
the  less  effective,  or  ineffective,  point  becomes  positive  to  the 
other. 

It    might   be    expected    that   the   normal   current  from    the 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  341 

muscles  below  the  skin  would  appear  unmistakably  at  the  moment 
at  which  both  leading- off  points  became  electrically  indifferent. 
This  seemed  in  fact  to  be  the  case  in  du  Bois'  experiments,  but 
the  P.D.,  strictly  speaking,  was  always  very  low,  and  gradually 
diminished.  This  last  fact  indicates  that  the  parelectronomy 
of  the  subcutaneous  muscles  was  abolished  by  the  gradual 
permeation  through  the  skin  of  the  ISTaCl  solution,  so  that  we 
seem  to  be  a  iniori  justified  in  supposing  that  the  very  first  signs 
of  the  normal  muscle  current  are  also  due  to  corrosion  of  the 
natural  transverse  section.  Hence,  as  Hermann  (10)  was  the 
first  to  point  out  and  demonstrate  directly  by  corrosion  with 
silver  nitrate,  which  perceptibly  alters  (darkens)  the  subjacent 
muscles,  this  experiment  cannot  be  held  conclusive  for  the  theory 
of  the  pre-existence  of  the  muscle  current.  "  If  the  points  of 
corrosion  are  so  chosen  that  there  is  no  subjacent  aponeurotic 
muscle-surface  {e.g.  the  outermost  points  of  the  toes,  and  skin  of 
back),  there  is  actually  no  deflection  corresponding  with  the 
muscle  current,  but  the  circuit  is  as  free  of  current  as  is  possible 
in  any  circuit  which  contains  moist  conductors  and  metals."  If 
creosote,  silver  nitrate,  or  still  better,  corrosive  sublimate,  are 
used  on  Hermann's  plan,  instead  of  the  rapidly  dissolving  salt 
solution,  it  is  really  possible  at  a  given  time  to  demonstrate 
complete  absence  of  current  between  the  two  principal  contacts 
with  the  skin,  while  later  on  corrosion  sets  in,  and  a  weak 
normal  current  is  produced.  In  fishes,  where  the  skin  current  is 
usually  less  strongly  developed  than  in  the  frog,  it  is  generally 
sufficient  to  keep  them  a  certain  time  in  water  at  the  temperature 
of  the  room  (Hermann)  to  produce  absence  of  current  on  leading 
off'  from  the  immobilised  uninjured  animal.  We  have  shown 
above,  when  describing  the  parelectronomic  condition,  that  it  is 
possible  to  obtain  a  completely  isolated  muscle  which  is  absolutely 
currentless,  and  du  Bois  himself  observed  the  same  repeatedly  on 
the  frog's  gastrocnemius.  That,  this  notwithstanding,  he  should 
still  maintain  the  pre-existence  of  muscle  currents,  was  principally 
because,  in  so  many  other  cases,  the  same  muscle  exhibits  small 
but  regular  differences  of  potential  in  spite  of  every  possible  pre- 
caution. We  must,  however,  accept  Hermann's  view  that  in  such 
cases  also  the  electromotive  action  depends  on  the  unobserved  en- 
trance of  injurious,  i.e.  chemically  disturbing,  fluids  (skin-secretion, 
muscle   juices,    etc.),    unequal    rise   of    temperature,    contact,   or 


342  ELECTRO-PHYSIOLOGY  chap. 

pressure,  which  can  only  be  avoided  by  complete  familiarity  with 
the  deleterious  matters  on  the  one  hand,  and  the  extraordinary 
sensibility  of  the  muscle -substance  on  the  other.  Above  all, 
contact  with  any  wound  in  the  muscle,  or  the  fluid  by  which 
this  is  moistened,  must  be  carefully  avoided.  Yot,  as  was  pointed 
out  by  du  Bois-Eeymond,  the  exposed  fibres,  dying  or  dead,  e.g.  in 
an  artificial  cross-section,  are  extremely  active  in  developing  cur- 
rent. These  facts  are  very  striking  in  regard  to  du  Bois'  dictum 
that  only  such  matters  as  attack  the  muscle-substance  chemically, 
and  thereby,  as  he  said,  destroy  the  parelectronomic  layer,  develop 
electromotive  action,  since  we  are  justified  in  assuming  that  the 
muscle -substance  itself  does  not  undergo  chemical  alteration. 
But  it  must  be  remembered  that  the  exposed  fibres  rapidly  set 
up  rigor,  and  undergo  chemical  changes,  which  of  course  develop 
acids.  Since,  on  the  other  hand,  it  is  known  that  even  very 
dilute  acids  are  highly  injurious  to  the  vital  properties  of 
muscle,  it  is  natural  to  refer  the  current-developing  property  of 
the  artificial  cross-section  to  the  acidifying  of  the  muscle-substance. 
How  far  this  assumption  is  really  justifiable  must  be  decided  later. 
The  theory  of  pre-existence  of  electromotive  action  meets 
with  special  dihiculties  in  the  uninjured,  or  apparently  uninjured, 
adductor  group  of  the  frog.  In  the  majority  of  cases  du  Bois 
found  a  descending  current  between  the  two  ends  of  tendon, 
but  there  were  also  cases  of  complete  absence  of  current,  as 
well  as  of  a  reversed  current.  The  current  between  upper 
end  of  tendon  and  equator  (du  Bois'  "  upper  current ")  was 
greater,  as  a  rule,  than  that  between  equator  and  lower  end  of 
tendon  ("lower  current").  Yet  du  Bois  also  found  the  opposite, 
there  being  even  cases  in  which  both  ends  of  tendon  were  positive 
to  the  equator.  These  discrepancies  and  confusions  were,  as 
Hermann  points  out,  sufficient  in  themselves  to  shake  the  par- 
electronomic theory ;  but  such  was  not  the  case.  On  the  con- 
trary, on  the  ground  of  certain  results  with  the  adductor  muscles 
it  obtained  a  wider  extension  from  the  presimiption  of  a 
parelectronomic  strip,  developed  in  many  cases  in  place  of 
the  parelectronomic  layer  (11).  By  this  du  Bois-Eeymond 
designated  the  (rare)  case  in  which  an  artificial  section  in  the 
neighbourhood  of  the  end  of  the  tendon  is  positive,  and  not,  as 
usual,  negative,  to  the  longitudinal  section.  It  will  be  shown 
later  that  all  these  irregularities  admit  of  a  simple  explanation  ; 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  343 

for  the  moment  we  can  only  say  that  the  muscles  of  the  frog's 
thigh,  e.g.  sartorius,  may  be  oljtained  perfectly  free  from  current 
without  much  difficulty  (16).  The  proof  that  skeletal  muscle 
can  always  be  obtained  free  of  current  with  proper  precautions 
does  not,  however,  exhaust  the  evidence  against  electromotive 
action  in  uninjured  muscle.  In  1874  Engelmann  (12)  pointed 
out  that  the  heart  is  a  muscle  peculiarly  well  adapted  to  in- 
vestigation in  the  normal,  uninjured  condition.  Experimentally, 
indeed,  with  every  variety  of  lead-off,  it  gives  no  current.  It 
is,  however,  obvious  that  an  artificial  section  of  the  heart  must 
be  as  negative  as  that  of  any  other  muscle ;  and  it  was  with 
knowledge  of  this  that  Matteucci  constructed  a  battery  of  pigeons' 
hearts  with  transverse .  sections.  It  is  interesting  relatively  to 
the  theory  of  the  longitudinal  sectional  current  that  (Engelmann, 
12)  the  E.M.r.  between  the  artificial  transverse  section  and 
natural  surface  of  cardiac  muscle  declines  very  rapidly.  This  is 
the  more  striking  since  it  has  long  been  known  (as  pointed  out 
by  du  Bois)  that  the  longitudinal  current  of  monomerous  skeletal 
muscle,  when  once  developed,  is  singularly  constant.  Engelmann 
found,  e.g.,  that  the  E.M.F.  in  the  sartorius  in  1  hour  fell  to 
81-1  %,  in  24  hours  to  43-6  %,  and  in  48  hours  to  30-8  % 
(average  of  45  experiments).  Eenewing  the  section,  i.e.  application 
of  a  fresh,  deeper  cross-section,  is  usually  of  little  use,  leading  at 
most  to  a  slight  augmentation  of  the  muscle  current.  In  the 
heart  the  results  are  very  different.  Here  refreshing  the  old 
section  is  sufficient  to  restore  the  E.M.F.  to  its  original  vigour. 
Hence  it  might  appear  as  though  the  development  of  the  parelec- 
tronomic  layer  could  be  directly  observed  in  this  case.  The  fact, 
however,  is  easily  interpreted,  considering  the  analogous  behaviour 
of  i^olymerous  skeletal  muscle.  Two  long  muscles,  divided  into  many 
short  segments  by  tendinous  intersections,  run  along  the  inner  side 
of  the  body-wall  of  Salamandra  maculata.  If  such  a  band-shaped 
muscle  is  excised,  divided  transversely  through  a  single  segment, 
and  protected  from  drying,  it  will  be  found  infallibly  that  after 
some  time  this  injured  segment  alone  shows  symptoms  of  rigor, 
while  the  rest  retain  their  normal  appearance  and  excitability, 
i.e.  mortification  has  been  arrested  at  the  nearest  tendinous  inter- 
section. On  leading  off  from  such  a  muscle  to  the  galvanometer, 
on  the  one  side  from  an  artificial  cross-section,  on  the  other  from 
any  point  of  the  muscle  surface,  a  normal  current  will  of  course 


344  ELECTRO-PHYSIOLOGY  chap. 

appear  immediately  after  making  the  artificial  section.  According, 
however,  to  the  pre-existence  theory,  this  would  still  be  demon- 
strable if  the  injured  segment  were  completely  rigored,  since 
there  would  then  be  an  unequal  lead-off  from  the  natural 
cross-section  of  the  next  segment,  as  in  the  tendon  or  bones  of  a 
monomerous  muscle.  But  this  is  not  the  case ;  the  longitudinal 
sectional  current  only  lasts  so  long  as  a  portion  of  the  substance 
of  the  segment  provided  with  an  artificial  cross-section  is  living ; 
it  becomes  nil  when  this  segment  is  completely  rigored,  and  only 
recovers  its  former  proportions  when  a  new  section  is  made  on 
the  farther  side  of  the  tendinous  intersection. 

Analogous  relations  exist  in  cardiac  muscle.  This  stands 
apart  from  other  striated  muscle  not  only  in  regard  to  the  com- 
plicated character  of  its  fibres,  which  is  here  of  no  importance, 
but  also  with  reference  to  the  much  smaller  dimensions  of  its 
morphological  elements,  which  consist  of  minute,  microscopic  cells. 
Engelmann  showed  that  the  single  cells  of  cardiac  muscle  proved 
themselves  in  dying  to  be  perfectly  separate  individuals,  exactly 
resembling  the  single  constituents  of  polymerous  muscle.  The 
process  of  rigor  induced  by  section  originates  in  the  heart  at 
a  very  short  distance  from  the  wound,  and  therefore  occurs  more 
quickly  than  in  normal  muscles  with  long  fibres,  so  that  here,  as 
in  polymerous  skeletal  muscle,  the  margin  between  dead  and 
living  muscle  substance  is  formed  in  the  last  resort  by  the 
natural  surfaces,  or  ends,  of  the  cells  not  directly  injured.  If, 
notwithstanding  these  data,  the  standpoint  of  the  pre-existence 
theory  is  adopted,  there  is  nothing  for  it  but  to  assume  that 
each  single  cell  of  cardiac  muscle  is  furnished  at  its  ends  with  a 
parelectronomic  layer,  just  as  in  polymerous  muscle  a  parelec- 
tronomic  layer  must  be  assumed  on  either  side  of  the  tendinous 
intersection.  But  such  a  conclusion  will  hardly  be  subscribed 
to,  unless  inevitable.  It  follows  therefore  from  the  reaction  of 
polymerous  and  cardiac  muscle,  that  both  the  constituents  of 
the  former,  and  the  cell  elements  of  the  latter,  give  no  external 
electromotive  response  in  the  uninjured  state. 

Analogous  experiments,  undertaken  by  Engelmann  on  the 
organs  composed  of  smooth  muscle  cells,  yielded  the  sam.e  results. 
Here  too,  as  in  the  heart,  the  E.M.F.  sinks  very  rapidly  between 
artificial  transverse  and  natural  longitudinal  section,  rising  again 
when   the    section   is    refreshed,  a   reaction  which    may  also    be 


ELECTROilOTIVE  ACTIOX  IX  MUSCLE 


witnessed  in  the  adductor  muscle  of  Anodonta.  Each  muscle- 
cell  must  therefore  be  regarded  as  free  from  current  in  the 
uninjured  state.  If  the  longitudinal  current  disappears  entirely 
on  injuring  a  polymerous  muscle  when  the  progress  of  rigor  is 
arrested  at  the  nearest  tendinous  intersection,  the  question  arises 
whether  there  is  no  means  of  limiting  the  invading  process  of 
mortification  from  the  artificial  cross-section  in  a  monomerous 
muscle,  and  thus  abolishing  the  muscle  current.  The  excised 
muscle  cannot  possibly  be  saved,  but  it  is  conceivable  that  if 
circulation  were  maintained,  a  muscle  cut  transversely  might 
heal  up  again.  Engelmann  {I.e.)  found  in  fact  that  ordinary 
skeletal  muscle  (frog's  sartorius)  did  become  gradually  current- 
less  again  after  subcutaneous  incisions ;  if  the  artificial  section 
loses  its  negative  potential  under  the  influence  of  normal  condi- 
tions of  nutrition,  the  natural  ends  of  the  fibres,  during  life, 
could  certainly  not  be  the  seat  of  electromotive  action. 

All  these  facts  concur  to  show  that  striated  muscles  are 
free  from  current  when  perfectly  uninjured,  and  that  the  "  current 
of  rest  in  muscle  "  implies  the  existence  of  artificial  cross-sections, 
mechanical,  thermic,  or  chemical. 

Passing  to  the  different  attempts  at  explanation  of  electro- 
motive action  in  the  injured  "  resting "  muscle,  it  must  in  the 
first  place  be  remarked  that  one  of  the  two  theories  which  till 
recently  stood  in  sharp  contrast  must  now  be  regarded  as  dis- 
proved, at  least  in  the  form  in  which  it  was  originally  pro- 
pounded by  du  Bois-Eeymond.  Since  Hermann's  epoch-making 
work,  the  view  has  more  and  more  gained  ground,  that  in  the 
complicated  processes  within  the  living  substance,  chemical  action 
deserves  at  least  as  much  attention  as  the  physical  symptoms, 
and  that  from  any  one  given  phenomenon  it  is  not  permissible 
to  draw  a  parallel  between  tissue  {e.g.  living  muscle  or  nerve) 
and  a  purely  physical  schema,  and  to  treat  it  on  this  assump- 
tion. Yet  on  account  of  its  historical  interest,  as  well  as  in 
regard  to  future  discussion,  we  must  give  a  brief  account  of  du 
Bois-Eeymond's  "  molecular  theory "  ;  the  more  so  because  an 
attempt  has  recently  been  made  to  revive  it,  although  in  a 
different  form  (Bernstein).  Moreover,  it  gives  an  opportunity  of 
discussing  some  facts  that  are  important  to  the  sequel,  with 
regard  to  the  distribution  of  current  in  animal  conductors. 

If  a  body,  such  as  the  transversely  bisected  muscle,  is  the 


346 


ELECTRO-PHYSIOLOGY 


seat  of  electromotive  energy,  the  first  essential  is  to  ascertain 
its  distribution  of  potential.  How  this  can  be  effected  with 
the  help  of  a  homogeneous,  leading -off  circuit,  i.e.  one  which 
in  itself^  and  by  its  application  to  the  moist  conductor,  develops 
no  differences  of  potential  on  contact  with  the  surface  of 
the  electromotive  conductor,  has  already  been  stated.  It 
remains  to  show  how  far  conclusions  may  be  drawn  from  the 
distribution  of  surface  potential  as  to  the  internal  electrical 
conditions.  Starting  with  the  consideration  of  a  regular  column 
of  fluid,  in  the  centre  of  which,  at  any  point  of  its  axis,  an 
electromotive  force  is  in  action,  the  lines  of  current  in  the 
plane  of  any  longitudinal  section  may  be  represented  by  the 
accompanying  diagram  (Fig.  108). 


Fig.  108. — Diagram  of  current  distribution  in  a  column  of  fluid.     (Rosenthal.) 


If,  e.g.,  (A)  represents  a  small  body  composed  of  two  different 
metals  in  contact,  the  entire  column  will  be  traversed  by  lines 
of  current  in  the  direction  of  the  outgoing  arrows,  which 
collectively  form  a  series  of  planes  (planes  of  current)  lying 
one  within  the  other.  Corresponding  with  the  "  fall  of  potential  " 
there  will  be,  at  each  point  of  the  path  of  current,  a  positive,  or 
negative,  potential,  and  it  is  easy  to  conceive  a  second  system  of 
lines  or  planes  if  each  equi-potential  point  on  the  different  lines 
or  curves  of  current  (planes  of  current)  is  joined  together,  as 
indicated  by  the  dotted  lines.  '  These  last  curves,  in  which  the 
intensity  of  current  diminishes  in  proportion  with  increasing 
resistance — as  they  approach  the  surface  of  the  column  —  are 
known  as  curves  of  potential,  or  isoelectric  curves,  which  again 
form  collectively  a  system  of  curved  planes  (planes  of  potential, 
isoelectric  j^l^nes),  cutting  the   planes   of  current  at  right   angles. 


ELECTROMOTIVE  ACTION  IN  MUSCLE 


347 


Here,  as  in  the  regular  muscle  cylinder,  the  lines  of  intersection 
of  the  isoelectric  planes  with  the  surface  of  the  column,  form 
circles  parallel  with  the  periphery  of  the  end-surfaces,  the  curves 
of  current  of  meridional  lines.  Yet  a  perfectly  definite  seat 
of  electromotive  force  cannot  be  forthwith  determined,  for  an 
analogous  distribution  of  surface  potential  may  occur  in  many 
other  cases,  where  it  is  at  least  doubtful  whether  electromotive 
forces  are  at  work  within  the  body  at  only  one,  or  at  several,  or 
many  places.  As  a  matter  of  fact,  each  new  seat  of  electro- 
motive action  implies  a  different  system  of  lines  of  current  and 
potential,  i.e.  a  different  distribution  of  surface-potential ;  but,  as 
Helmholtz  pointed  out,  seeing  that  in  a  complex  of  electro- 
motive forces  the  potential  of  each  point  on  the  surface  of  the 


+    -I-      -)-      +     .4 


Fig.  109. — Schema  of  hypothetical  distribution  of  electromotive  planes  in  a  muscle-fibre. 
Axial  longitudinal  section.     (Hermann.) 


body  corresponds  with  the  sum  of  the  potentials  brought  into  play 
at  this  particular  point  by  each  electromotive  force  respectively, 
we  may  conceive  many  combinations  in  which  the  same  distribu- 
tion of  surface-potential  would  always  present  itself.  Turning 
now  to  the  case  in  which  a  cylindrical  body  exhibits  a  similar 
electromotive  action  to  that  which  occurs  at  both  ends  of  a 
muscle  with  parallel  fibres,  provided  at  either  end  with  an 
artificial  transverse  section,  we  find  (amongst  others)  that  a 
solid  copper  cylinder  with  a  zinc  sheath  corresponds  with  the 
required  conditions  when  immersed  in  any  conducting  fluid, 
e.g.  dilute  H^SO^.  This,  according  to  schema  A  (Fig.  109),  is 
traversed  by  innumerable  lines  of  current,  which  pass  as  a  whole 
from  the  electrically  positive  zinc  sheath  to  the  electrically  nega- 
tive end-surfaces  of  the  copper,  exhibiting  a  distribution  of  surface- 


348 


ELECTRO-PHYSIOLOGY 


potential  analogous  with  that  of  the  muscle  prism.  But  the 
same  result  would  ensue  with  two  other  presumptive  dispositions 
of  the  electromotive  planes.  A  hollow  cylinder,  e.g.,  the  surface 
of  which  is  coated  with  zinc,  may  be  filled  with  acid  water,  the 
entire  apparatus  being  immersed  in  the  same  :  schema  B  (I.e.)  will 
then  correspond  with  the  distribution  of  potential.  Lastly,  if  a 
hollow  zinc  cylinder  with  copper  end-surfaces  is  examined  under 
the  same  conditions,  schema  C  will  become  effective  (Fig.  109). 

Which  of  these  three  schemata  is  actually  realised  in  the 
muscle  cannot  jj^riw^a  facie  be  determined  by  experiment.  In 
regard  to  the  first,  it  must  be  further  observed  that  (in  the  sense 
of  the  preceding  observations)  the  one  solid  cylinder  may  be 
replaced  by  any  number  of  little  cylindrical  or  rounded  bodies 
{" perijjolar  ■molecules"),  each  provided  with  positive  longitudinal, 
and   negative   transverse,   sections,   provided   they   are   regularly 


Fig.  110.— Schema  of  peripolar  («)  and  dipolar  (h)  molecnles.     (Hermann's  Handh.  i.  1.) 
Parelectrononiic  molecules  at  natural  section. 

arranged  somewhat  after  the  accompanying  diagram  (Fig.  110,  cc). 
With  reference  to  the  real  anatomical  relations  of  the  muscle,  the 
first  case,  in  the  modified  form  last  stated,  coincides  with  the 
molecular  theory  of  du  Bois-Eeymond,  the  second  with  a  hypo- 
thesis of  G-riinhagen,  which  postulates  an  electromotive  opposi- 
tion between  muscle -fibrils  and  surroimding  nutritive  fluids, 
while,  finally,  the  third  is  fundamental  to  Hermann's  alteration 
theory,  which  presumes  that  electromotive  action  is  set  up  at  the 
artificial  transverse  section. 

If  any  two  points  of  different  potential  upon  the  neutral 
sheath  are  joined  by  a  deriving  circuit,  a  branch  of  the  current 
will  flow  into  this  circuit,  corresponding  with  a  fraction  of  the 
internal  E.M.F.,  since  these  currents,  particularly  in  the  imme- 
diate vicinity  of  the  electromotive  planes,  undergo  a  large 
amount  of  short  circuiting.  Therefore,  as  already  urged  by 
Hermann,  it  is  important  in  many  cases  to  take  into  considera- 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  349 

tioii  that  the  internal  current  can  by  no  means  be  neutralised  by 
compensation  of  the  led- off  portion  of  the  current.  "  A  muscle 
with  a  deriving  circuit,  of  which  the  current  is  compensated, 
behaves  as  though  the  circuit  were  non-existent,  and  the  cur- 
rents completed  themselves  in  the  substance  of  the  muscle." 
Du  Bois-Eeymond's  comprehensive  physical  theory  of  the  cur- 
rent in  muscle  (and  nerve)  starts  from  the  fact  that  every 
particle  of  muscle  that  it  is  possible  to  examine,  exhibits 
the  same  normal  differences  in  potential  between  longitudinal 
and  transverse  section.  Thus  nothing  prevents  us  from  pictur- 
ing the  whole  muscle  and  each  single  fibre  as  consisting  of 
many  little  particles  or  molecules,  every  one  of  which  has 
the  same  electromotive  action  as  the  entire  muscle  cylinder. 
These  may  either  be  conceived  as  spheres  wdth  two  negative 
polar  zones  and  a  positive  equator  (peripolar  molecules),  or, 
as  du  Bois-Reymond  assumed  later  in  view  of  certain  facts 
to  be  discussed  below,  as — in  each  peripolar  electromotive 
molecule — consisting  of  two  dipolar  portions,  of  which  the 
positive  halves  are  convergent  (Fig.  110,  V).  Accordingly,  each 
artificial  cross-section  would  fall  between  two  jDOsitive,  never 
between  two  negative,  planes.  For  the  rest  it  is  quite  imma- 
terial what  aspect  we  give  to  the  individual  molecules,  they  may 
as  well  be  imagined  discs  as  spheres.  The  regular  arrangement  of 
them,  according  to  the  accompanying  diagram  (Fig.  110),  is  the 
sole  essential.  If  now  the  whole  cylindrical,  or  prismatic,  aggre- 
gate of  these  same  electromotive  molecules  is  conceived  as 
surrounded  by  a  thin  sheath  of  some  indifferent  conductor  (peri- 
mysium, sarcolemma,  dead  layer  at  the  cross-section),  the  distribu- 
tion of  potential  at  the  surface  will,  as  has  been  shown,  correspond 
throughout  with  the  real  experimental  conditions.  With  the  aid  of 
this  hypothesis  it  is  possible  indeed  to  give  a  simple  explanation 
of  all  phenomena  of  the  "  current  of  rest "  in  the  muscle,  more 
particularly  the  fact  of  the  homodromous  activity  of  each  least 
particle  of  muscle,  as  well  as  tlie  so-called  "  jSTeigungstrom  "  in 
oblique  sections.  The  interpretation  of  parelectronom}",  however, 
presents  difficulties  which,  on  the  j) re  -  existence  theory,  can 
only  be  explained  by  the  further  assumption  as  above,  that 
a  specific  compensating  layer  is  situated  at  the  natural  trans- 
verse section,  figured  by  du  Bois  -  Pteymond  as  consisting 
of    "  parelectronomic    molecules,"    whose    positive    surfaces    turn 


350 


ELECTRO-PHYSIOLOGY 


towards  the  tendon,  and  may  be  derived  from  the  inner  half  of 
the  externally  situated  dipolar  molecules.  When  the  parelectro- 
nomic  layer  consists  of  a  whole  series  of  dipolar  molecules 
arranged  in  columns  a  "  parelectronomic  tract "  results.  Bern- 
stein (13)  has  recently  modified  du  Bois'  molecular  theory  in 
certain  essential  particulars,  endeavouring  to  give  it  a  new  basis 
as  the  "  electro-chemical  violecuktr  theori/."  According  to  him  the 
living  fibres  must  be  presumed  "to  consist  of  a  longitudinal  series  of 
molecules,  aggregated  into  fibrils  of  a  finite  diameter,  lying  in  a 
congruent  fluid,  from  which  they  derive  their  nutrition  (para- 
plasma)."  They  are  linked  together  by  forces,  "  which  may  be 
regarded  as  identical  with,  or  akin  to,  chemical  aftinity,"  and 
consist  of  a  nucleus  of  complex  chemical  constitution,  identical 
with  Pfliiger's  living  molecule  of  albumen.      The  long  sides  of 


the  molecular  nucleus  (31),  conceived  as  a  prism  (as  in  Fig.  Ill), 
the  end- surfaces  being  linked  together  loosely  by  atoms  of  oxygen, 
are  described  by  Bernstein  as  "  laden  with  oxydisable  non-nitro- 
genous groups  of  atoms,  comparable  with  fine  platinum  wires, 
dipping  into  an  atmosphere  of  hydrogen."  "  The  rows  of  mole- 
cules, bathed  in  nutritive  fluid,  constantly  draw  out  of  it  the 
charges  essential  to  metabolism."  "  If  these  are  regarded  as 
electro-positive  in  relation  with  the  molecular  nucleus,  the  oxygen 
atoms  on  the  other  hand  as  electro-negative  charges  of  the  same, 
the  current  of  rest  in  the  muscle  (and  nerve)  results  when  the 
longitudinal  surface  is  connected  with  an  artificial  cross-section. 
It  may  also  be  assumed  that  on  making  an  artificial  section  the 
tearing  apart  of  the  chain  of  molecules  sets  free  assimilated 
oxygen,  which  would  be  negative  in  potential  to  the  molecular 
nucleus."  The  parelectronomic  condition  of  the  ends  of  tendon 
would  be  explicable  on  this  theory,  if  it  is  assumed  "  that  each  such 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  351 

series  of  molecules  constantly  passes  over  into  the  adjacent  series 
by  a  loop-like  circuit,  and  thus  presents  no  free  cross-section." 
If  a  single  such  "  molecule,"  or  better,  aggregate  of  molecules,  lay 
singly  embedded  in  a  conducting  fluid,  it  would  evidently  react 
in  every  particular  like  a  peripolar  molecule  of  du  Bois ;  collect- 
ively; however,  these  cannot,  like  the  latter,  be  conceived  as  sur- 
rounded by  molecular  currents,  since  the  potential  on  all  sides 
seems  to  be  neutralised.  The  same  objections  as  obtain  against 
the  original  molecular  theory  also  to  a  great  extent  apply  to  its 
"  electro -chemical"  translation,  while  the  excessively  detailed 
presumptions  of  the  latter  re  chemical  structure  of  living  sub- 
stance must  a 'priori  give  rise  to  miich  reflection. 

According  to  Griinhagen's  theory,  we  must  assume  an  electro- 
motive opposition  between  each  primitive  fibril  and  the  surround- 
ing nutritive  fluid  (sarcoplasma),  whereby  the  latter  represents 
the  positive,  the  fibrils  the  negative,  link  of  the  chain.  The 
absence  of  current  in  uninjured  muscles  would,  on  this  theory, 
be  very  simply  explained  by  the  immersion  of  the  negative 
electrical  fibrils  in  the  positive  nutritive  fluid.  Griinhagen's 
views  of  the  cause  of  electromotive  action  in  animal  tissues 
originated  in  experiments  with  porous  cylinders.  Yet,  as  Her- 
mann points  out,  it  is  difficult  to  see  how  these  experiments 
apply  to  the  given  relations  in  muscle.  Grlinhagen  found, 
namely,  that  cylindrical,  porous  bodies,  during  the  moistening  of 
their  cross-sections  (end-surfaces),  exhibited  difference  of  electrical 
potential  towards  points  in  the  middle  of  their  longitudinal  sur- 
face, and  also  between  asymmetrical  points  of  the  two  surfaces 
in  themselves — in  the  same  direction  as  the  muscle  cylinder. 
These  differences  of  potential  disappear  when  the  porous  cylinder 
is  saturated  with  fluid,  and  is  therefore  to  l)e  viewed  as  an  effect 
of  the  'passage  of  fluids  through  the  porous  substance.  Grlinhagen 
imagines  the  relation  between  fibrils  and  surrounding  nutritive 
fluids  to  be  similar. 

The  third  theory  relative  to  the  seat  of  electromotive  action 
is  the  alteration-theory  of  L.  Hermann,  which  is  in  perfect  agree- 
ment with  all  the  facts  known  to  us.  This  theory  refers  all  electro- 
motive activities  of  living  tissue  to  chemical  changes  of  the 
substance  without  regard  to  its  molecular  structure.  With 
reference  to  the  "resting"  muscle  current,  the  theory  proceeds  from 
the  postulate,  "that  dying  substance  is  negative  to  living  substance." 


352  ELECTRO-PHYSIOLOGY  chap. 

The  seat  of  electromotive  action  must  accordingly  be  referred  to 
the  margin  between  dying  and  living  substance  ("  demarcation 
surface  ").  Hermann  therefore  designates  the  "  current  of  rest  " 
in  the  muscle,  the  "demarcation  current."  Hering  (14)  has 
recently  expounded  Hermann's  principle  of  interpretation  on  very 
general  considerations.  The  proposition  that  uninjured  resting 
muscle  or  nerve  has  no  current  implies  to  him  "  that  such  a 
tissue  does  not  develop  a  current  that  can  be  led  off  externally,  so 
long  as  its  metabolism,  i.e.  the  internal  chemical  action  in  all  its 
parts,  is  equal.  Every  disturbance  of  equilibrium  sets  up  currents 
that  can  be  led  off."  Hering  also  emphasises  the  fact  already 
brought  forward  by  Hermann,  that  alteration  of  chemical  action 
in  any  part  of  the  living  continuum  may  appear  not  merely  "  in 
that  the  part  concerned  becomes  negative  to  the  unaltered  parts, 
but  also  that  it  may  become  positive  to  the  same."  If  then  the 
part  that  differs  chemically  from  the  remaining  substance  is 
termed  (relatively)  altered,  we  must  distinguish  between  "  a 
{relatively)  i^ositive  and  a  {relatively')  negative  alteration"  to  which 
must  be  added  that  "  the  alteration  is  characterised  not  by  altered 
chemical  composition,  but  by  altered  chemical  action,  which  may 
of  course  give  rise  to  altered  composition."  As  has  been  shown 
in  another  section  {e.g.  fatigue  in  muscle),  Hering  distinguishes 
in  every  living  substance  between  the  ascending  alteration,  the 
descending  alteration,  and  the  state  of  equilibrium. 

"  Both  '  up '  and  '  down '  changes  may  occur  with  very 
different  rapidity,  according  as  the  strength  of  assimilation 
exceeds  that  of  dissimilation,  or  vice  versa,  to  a  greater  or 
less  extent.  If  all  parts  of  a  living  continuum  are  equi- 
potential,  or  if  they  alter  with  the  same  rapidity  in  an  ascend- 
ing or  descending  direction,  no  current  that  can  be  led  off  will 
be  produced.  Each  variation  in  rapidity,  or  direction  of 
alteration,  will,  however,  produce  a  current  that  can  be  led  off. 
Accordingly,  we  may  conceive  every  variation  in  rapidity  of 
the  positive  or  negative  alteration,  as  arranged  in  a  series, 
so  that  the  quickest  ascending  change  formed  the  upper,  so 
to  say,  positive — the  quickest  descending  change,  the-  lower,  so 
to  say,  negative  end  of  the  series.  If  two  portions  of  a  living 
continuum  which  give  different  chemical  reactions  are  connected 
by  an  external  conductor,  they  will  ceteris  paribus  yield  a  stronger 
current  in  proportion  with  the  distance  between  the  two  leading- 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  353 

off  points  in  the  series  mentioned,  and  the  positive  current 
always  flows  through  the  external  circuit  from  the  point  nearest 
the  positive  end  of  the  series  to  that  which  is  nearest  the 
negative  end.  This  is  the  laiv  of  all  vital  currents  in  nerve  and 
muscle. 

"  A  sartorius  exposed  with  all  possible  precaution,  e.g.  one 
that  is  no  longer  normally  nourished,  undergoes  a  slow  and 
steady  descending  alteration,  because  dissimilation  preponderates 
over  assimilation;  it  is  slowly  dying. 

"  If  this  descending  change  proceeds  in  every  part  at  exactly 
the  same  rapidity,  the  most  sensitive  galvanometer  will  fail 
to  detect  any  current.  This  ideal  case  is  never  of  course 
fully  realised.  But  with  even  a  moderately  sensitive  galvano- 
meter, no  current  will  be  detected  in  such  a  muscle,  as  was 
shown  by  du  Bois-Eeymond,  as  well  as  later  observers.  On 
making  a  cross-section  in  the  muscle,  a  more  rapid  descending 
change  at  once  appears  in  the  muscle-substance ;  the  part  im- 
mediately adjacent  to  the  section  mortifies.  This  dead  part 
is  no  longer  included  in  the  living  continuum,  and  must  be 
regarded  as  an  inessential  appendage.  The  more  rapid  '  down ' 
change  and  mortification,  however,  proceed  ^jar-i  ^jass?^  along  the 
fibre,  as  may  be  verified  under  the  microscope,  and  after  making 
a  transverse  section,  there  is  always  a  more  rapid  descending 
alteration  than  in  the  other  fibres.  The  cross-section  is  therefore 
negative  to  the  longitudinal  surface  of  the  muscle." 

But  it  is  not  merely  by  theoretical  considerations,  in  addi- 
tion to  its  extreme  simplicity,  that  the  Hermann-Hering  theory 
is  distinguished  frona  all  others.  There  are  also  direct  experi- 
mental facts  in  its  favour,  which  may  be  taken  as  proven.  Among 
these,  apart  from  all  previous  experiments  on  the  absence  of 
current  in  uninjured  muscles,  is  that  by  which  Hermann  tries  to 
determine  the  question  whether  the  development  of  the  demarca- 
tion current,  on  making  an  artificial  cross-section,  takes  a  percep- 
tible time,  or  whether  the  full  value  of  the  P.D.  between  longi- 
tudinal and  transverse  section  is  reached  immediately  after 
injury,  as  must  necessarily  be  the  case  under  the  presumption 
of  pre -existence  of  electromotive  forces.  For  this  purpose 
Hermann  constructed  a  "  fall "  rheotome,  in  which  the  expansion 
of  the  tendo  achilles  was  torn  away  from  the  gastrocnemius  by 
a   heavy  falling  body,    the    galvanometer    circuit    being   simul- 

2  A 


354  ELECTRO-PHYSIOLOGY  chap. 

taneously  closed  for  a  short  period.  If  this  closure  is  eftected 
once  at  the  moment  of  injury,  and  again  after  making  the  section, 
the  deflection  in  the  latter  case  will  be  greater  than  in  the  former, 
from  which  a  "  period  of  development "  of  the  muscle  current 
may  be  concluded.  Hermann  carried  out  similar  experiments 
with  the  same  results  on  muscles  with  parallel  fibres  (15). 

The  correctness  of  these  theoretical  presumptions  as  to  the 
causes  of  animal  (and  vegetable)  electrical  currents,  and  the  justi- 
fication for  rejecting  every  molecular  hypothesis  whatsoever,  are 
attested  by  the  author's  demonstration  of  the  direct  dependence 
of  the  muscle  current  on  local  cliemiccd  changes  in  its  suhstance.  If 
it  is  correct  that  in  muscles  and  nerves,  as  in  other  animal  and 
vegetable  tissues  also,  the  electrical  differences  of  potential  which 
may  be  demonstrated  under  certain  conditions  may  always  be 
traced  in  the  last  resort  to  the  different  chemical  reactions 
between  adjacent  parts  of  the  living  substance,  it  must  a  i^riori 
be  granted  as  possible  that  the  resulting  electromotive  action  can 
be  neutralised  again,  in  so  far  as  there  has  not  been  such  total 
destruction  as  to  prevent  restoration  of  the  normal  activity  of 
the  chemically  altered  substance.  It  is  known  that  even  excised 
muscle  possesses  to  a  certain  extent  the  capacity  of  readjusting 
chemical  changes  in  its  substance,  produced  by  certain  excitants 
(stimulants),  e.g.  "  recovery  "  in  "  fatigued  "  muscle.  We  liaA^e 
already  drawn  attention  to  the  interest  of  the  fact  that,  in- 
dependent of  previous  excitation,  a  muscle  may  be  thrown  into 
a  state  resembling  fatigue  by  submitting  it  to  the  action  of 
certain  chemical  substances  ("  fatigue-substances "),  after  which, 
by  washing  these  out  with  an  indifferent  fluid,  it  can  be  restored 
to  its  normal  excitability  (Eanke).  It  then  becomes  essential  to 
investigate  how  far  electromotive  action  may  result  from  the 
contiguity  of  fibres  which  are  chemically  altered,  but  still  capable 
of  recovery,  and  fibres  that  are  in  normal  chemical  activity. 
Eanke's  investigations  of  "  chemical  fatigue  of  muscle "  by 
salts  of  potash,  or  lactic  acid,  the  striking  effect  of  which 
upon  the  phenomena  of  polar  excitation  by  current  has  already 
been  discussed,  appear  to  promise  the  best  results.  It  is 
found  that  after  brief  immersion  of  one  end  of  a  sartorius  that 
is  free  from  current,  in  a  dilute  extract  of  muscle  tissue,  or 
highly  dilute  solutions  of  potassium  salts  (KNO^,  KH^PO^, 
KCl),  it  becomes  strongly  negative  towards  every  other  point  of 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  355 

the  muscle.  The  size  of  the  detiection  was  in  many  eases  a  little 
smaller  than  when  a  sartorius  provided  with  an  artificial  cross- 
section  is  connected  in  circuit  from  cut  surface  to  corresponding 
point  of  the  upper  surface.  Here  diminished  excitabihty  goes 
hand  in  hand  with  negativity  of  muscle-substance,  and  just  as 
this  may  be  simply  neutralised  by  washing  out  with  physiological 
NaCl  solution,  so  too  in  regard  to  current.  A  few  minutes 
suffice  to  reduce  the  P.D.  to  a  mere  trace,  which,  with  longer 
washing,  is  also  abolished,  so  that  the  muscle  is  once  more — 
as  at  the  beginning  of  the  experiment — free  from  current  and  of 
normal  excitability.  The  same  result  is  obtained  from  the  current- 
less  (parelectronomic)  gastrocnemius  by  painting  the  expansion 
of  the  tendo  achilles  with  fluid,  and  the  ascending  current 
obtained  in  consequence  is  well  developed  and  of  the  same 
order  as  the  normal  demarcation  current  (16).  This  very  fact, 
however,  makes  it  the  more  remarkable  that  the  "  potassium  cur- 
rent "  should  be  so  easily  neutralised  by  washing  out  with  an 
indifferent  fluid,  as  is  once  more  exhibited  in  a  striking  manner 
on  the  gastrocnemius ;  it  suffices,  after  the  muscle-substance  at 
the  tendo  achilles  has  become  strongly  negative  from  painting 
with  dilute  solution  of  potass -salt,  to  wash  it  for  a  few 
moments  with  3—4  %  NaCl  solution,  in  order  —  as  with  the 
galvanometer — to  replace  the  original,  currentless  condition. 
This  shows  that  the  prejudicial  effect  of  the  solution  can  only 
have  extended  to  the  extreme  ends  of  the  obliquely  inserted 
fibres.  From  these  experiments  the  current-developing  properties 
of  every  artificial  cross-section  of  a  muscle  are  also  easily  inter- 
preted, since  acid  potassium  phosphate  is  always  formed  when 
the  muscle-substance  becomes  rigored. 

In  opposition  to  the  "  potassium  currents,"  those  differences 
of  potential  which  appear  on  treating  currentless  muscle  in  the 
same  way  with  very  dilute  acid  solutions  {e.g.  lactic  acid)  seem  to 
depend  on  much  deeper  chemical  changes  in  the  muscle-substance, 
since  no  amount  of  washing  will  neutralise  them,  although  they 
are  weaker  than  those  produced  by  salts  of  potash. 

Du  Bois-Eeymond  laid  down  the  principle  that  no  more 
delicate  test  of  the  chemical  sensibility  of  the  muscle-substance 
to  any  fluid  can  be  devised  than  to  moisten  the  natural  cross- 
section  of  a  parelectronomic  muscle  with  the  solution,  and  to 
observe  the  changes  thus  produced  in  the  electrical  condition  of 


356  ELECTRO-PHYSIOLOGY 


the  section.  From  this  point  of  view,  the  potassium  salts  in 
general  must  be  regarded  as  distinct  muscle  poisons,  while  the 
corresponding  sodium  combinations  at  the  same  molecular  weight 
are  almost  innocuous,  and  even  possess  in  many  cases  a  distinct 
power  of  regenerating  excitability  (ISTa.^COg).  In  consideration  of 
this  last  fact  a  fluid  cannot  therefore  be  termed  indifferent  for 
the  muscle,  where  no  perceptible  current  is  developed  from 
its  local  application.  Even  the  physiological  NaCl  solution 
(0*5— 0"7  %)  which,  if  applied  for  hours  to  the  natural  cross- 
section  of  an  uninjured,  currentless  muscle,  causes  no  trace 
of  a  demarcation  current,  produces,  according  to  F.  S.  Locke 
(17),  a  visible  increase  of  excitability,  as  has  long  been  known 
with  regard  to  stronger  solutions.  Certainly,  however,  the 
current-developing  properties  of  a  solution  must  be  taken  as  the 
measure  of  its  injuriousness  to  the  muscle,  and  though  Nasse 
takes  a  0*7  %  solution  of  KCl  or  KNO^  as  equal  to  a 
0'2— 1'5  %  solution  of  NaCl,  his  conclusion  is  not  borne 
out  by  galvanometer  experiments.  If  the  lower  end  of  a 
curarised  sartorius  dips  into  even  a  2  %  solution  of  ISTaCl, 
no  perceptible  demarcation  current  will  have  appeared  after  10 
to  20  minutes,  or  there  may  even  be  a  faint  deflection  in  the 
opposite  direction,  in  the  sense  of  a  descending  current  in  the 
muscle.  Engelmann,  too,  found  in  his  investigations  into  the 
electromotive  properties  of  the  uninjured  surface  of  the  frog's 
heart,  that  solutions  of  NaCl,  if  stronger  than  0"6  %,  made 
the  points  in  contact  with  them  positive  in  regard  to  other  points 
of  the  surface  of  the  heart.  Still  less  deleterious  than  NaCl  is  the 
action  of  other  neutral  sodium  salts  upon  the  substance  of  the 
muscle,  e.q.  Na.SO,  and  !N"aNO„,  which,  even  in  strong  solutions 
(4—12  y^),  develop  only  a  small  amount  of  current,  as 
compared  with  the  local  effects  of  equivalent  solutions  of  JSTaCl  or 
the  corresponding  salts  of  K  upon  the  sartorius.  Even  alkaline 
sodium  carbonate,  which  augments  the  excitability  of  striated 
muscle  in  a  remarkable  degree,  either  produces  no  current  in 
dilute  solutions,  or  a  weak  inverted  current  only,  in  the  sense  of 
positivity  of  the  immersed  end  of  the  muscle  (18). 

The  opinion  generally  prevails  that  distilled  water  is  rapidly 
and  energetically  inimical  to  muscle-substance,  e.g.  Kiihne  con- 
cludes from  the  fact  that  a  frog's  sartorius  dipping  into  distilled 
water  loses  its  excitability  more  quickly  than  a  muscle  dipping 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  357 

for  the  same  time  into  nitric  acid  (xoW)'  ^^^^^  ^^^^  water  has  a 
quicker  destructive  action  than  the  dilute  acid,  and  du  Bois- 
Eeymond  states  that  a  gastrocnemius  dipping  into  distilled 
water  (15°  C.)  was  death-rigored  and  acid  within  an  hour. 
Consequently  one  might  have  expected,  if  the  development  of 
current  in  a  "  parelectronomic  "  muscle  depended  only  upon  the 
destruction  of  a  particular  layer  at  the  natural  cross-section,  that 
on  moistening  it  with  distilled  water,  a  powerful,  normal  current 
would  in  a  shorb  time  be  apparent,  since  it  is  proved  by  experi- 
ence that  the  current  -  developing  property  of  a  fluid  is  quite 
independent  of  its  conductivity.  This  is  partly  contradicted 
already  in  the  experiments  of  du  Bois  -  Eeymond,  since  the 
development  of  current  in  parelectronomic  muscles,  on  dipping 
them  into  distilled  water,  proceeds  weakly  and  sluggislily.  The 
sartorius  reacts  even  better.  If  the  knee-end  dips  into  water, 
an  increase  of  volume  is  perceived  in  it  shortly  after,  and  it  will 
then  regularly  be  found  weakly  'positive  to  points  of  the  normal 
surface.  After  longer  duration  of  the  action  of  water  (20— 
40  minutes)  the  muscle  section  is  much  swelled,  and  double  its 
former  breadth ;  it  looks  very  dark,  and  exhibits  all  the  external 
signs  of  rigor.  At  the  same  time  the  partially  rigored  muscle 
shows  as  little  electromotive  action  as  before,  or  there  may  still 
later  be  weak  signs  of  a  normal  demarcation  current.  Even  after 
hours  of  the  action  of  distilled  water,  the  demonstrable  P.D.  of 
the  two  sections  of  the  muscle  is,  in  spite  of  the  marked  differ- 
ences in  their  physical  properties,  relatively  insignificant,  and 
not  to  be  compared  with  those  which  underlie  the  normal 
demarcation  current  between  longitudinal  surface  and  artificial 
cross-section  (18). 

When  we  remember  that  all  known  methods  which  throw 
the  contractile  substance  of  the  muscle  into  rigor  (heating  to 
40°  C,  treatment  with  chloroform,  acids,  etc.),  produce  power- 
ful demarcation  currents  on  local  application,  the  absence  of 
electromotive  action  in  the  partially  water  -  rigored  sartorius 
is  very  significant,  since  it  would  appear  not  to  harmonise  with 
a  chemical  theory  of  the  muscle  current.  In  opposition  to  this 
it  must  be  remembered  that  the  condition  of  "  water  -  rigor " 
cannot  bo  immediately  identified  with  the  deep-seated  chemical 
alteration  of  the  muscle -substance,  due  to  spontaneous  or  sus- 
tained rigor,  or  to  heat-rigor.      This,  because  on  the  one  hand 


358  ELECTRO-PHYSIOLOGY  chap. 

the  acidity,  where  it  appears,  by  no  means  proceeds  jja^^i  ^9rtss26 
with  the  progressive  development  of  "  rigor,"  while  on  the  other 
the  possibility  of  recovery  of  excitability  in  water-rigored  muscles 
by  simple  dehydration  (2  %  NaCl  solution)  is  evidence  that  the 
coagulation  effects  are  of  another  kind  than  the  ordinary  forms 
of  rigor.  The  difference  between  water-rio'or  and  other  forms 
of  rigor  is  best  shown  by  the  fact  that  frog's  muscle,  in  an  ad- 
vanced stage  of  water-rigor  (an  hour  or  more),  exhibits  electro- 
motive action  in  the  same  sense  and  almost  in  the  same  degree 
as  uninjured  muscle.  If  the  lower  end  of  a  vertically  dependent 
sartorius  dips  for  30  minutes  into  distilled  water,  the  muscle 
will  usually,  as  stated  above,  show  no  current,  on  leading  off  from 
the  geometrical  equator  and  water-rigored  section,  or  it  exhibits 
a  weak  inverted  current.  But  if  part  of  the  moistened  muscle 
section  is  warmed  in  water  at  40°  C,  it  exhibits,  on  leading 
off,  the  same  electromotive  action  as  before ;  the  same  is. the  case 
after  crushing  or  cutting  the  water  -  rigored  end.  There  can 
therefore  be  no  doubt  that  there  is  chemically  a  fundamental 
difference  between  the  effect  of  the  rigor -like  condition  pro- 
duced by  distilled  water,  and  the  true  rigor -mortis  of  a  muscle, 
the  complete  development  of  which  seems  to  preclude  the  possi- 
bility of  electromotive  activity.  As  therefore  electromotive  function 
must  certainly  be  regarded  as  a  property  of  the  living  muscle,  it 
is  the  more  remarkable  that  it  should  in  no  way  be  bound  up 
with  the  continuance  of  all  vital  properties.  It  can  be  shown, 
i.e.  that  the  demarcation  current  persists  in  its  normal  direc- 
tion and  proportions  where  the  muscle  has  been  rendered  inexcit- 
able  by  chloroform,  ether,  or  amyl.  Eanke,  who  was  the  first  to 
make  these  observations,  always  exposed  the  whole  uninjured 
frog  to  the  vapour  of  the  anaesthetic,  and  examined  various 
stages  of  the  narcosis.  A  quicker  method  is  to  place  the  free 
sartorius,  with  an  artificial  cross-section,  along  with  the  leading- 
off  electrodes,  and  a  watch-glass  of  ether,  under  a  bell-jar  that  is 
not  too  small.  It  may  easily  be  seen  that  the  P.D.  between 
longitudinal  and  artificial  transverse  section  does  not  diminish 
to  any  perceptible  degree,  and  sometimes  even  appears  to  be 
augmented,  when  all  visible  manifestations  of  excitation  have 
failed  in  the  muscle  (19). 

While  contractility  and  conductivity  for  the  most  part  seem 
to    be    abolished     in    10  —  15    minutes,    but    little    diminution 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  359 

of  the  demarcation  current  can  be  observed,  even  after  hours  of 
exposure  to  ether  vapour,  vi^hich  is  the  more  remarkable  when  it 
is  considered  that  all  the  influences  which  depress  excitability 
have  also  a  general  diminutional  effect  upon  the  muscle  cur- 
rent. If  then,  during  ether  narcosis,  a  muscle — of  which  the 
excitability  seems  to  be  entirely  abolished — has  no  less  pro- 
nounced an  electromotive  reaction  than  under  normal  conditions, 
the  presumption  is  that  the  changes  in  chemical  activity  of  the 
muscle-substance,  which  must  always  be  reckoned  with  in  the 
proximity  of  a  cut  surface,  persist  during  the  ether  narcosis  to 
the  same  degree  as  under  normal  conditions.  Another  fact  of 
the  same  significance  is  that  local  treatment  with  salts  of  K  in 
correspondingly  dilute  solutions  also  renders  the  ether  muscle 
negative  at  the  point  of  contact.  Further,  remembering  the 
persistence  of  the  normal  physical  properties  of  the  narcotised 
muscle  at  a  time  when,  even  with  the  strongest  excitation,  there 
is  no  trace  of  visible  change  of  form,  it  does  not  appear  so 
surprising  that  a  muscle,  even  in  the  deepest  narcosis,  should  still 
be  capable  of  electromotive  response,  although  some  of  its 
normal  vital  properties  may  be  fundamentally  affected  or  entirely 
abolished.  For  if  it  is  admitted  that  the  "  current  of  rest "  owes 
its  origin  to  a  partial  "  alteration "  in  the  substance,  it  would 
follow  that  it  may  be  expected  in  all  those  cases  in  which  the 
preparations  concerned  have  not  been  fundamentally  disturbed  in 
their  normal,  chemical  composition  ;  and  this  both  in  respect  of 
ether,  and  of  turgescence  of  the  muscle  from  water.  Later  on 
we  shall  have  to  discuss  other  facts  which  indicate  that  con- 
ductivity and  contractility  of  the  muscle  are  primarily  abolished 
by  narcosis,  while  local  excitability  persists  in  the  sense  that 
certain  chemical  changes  still  occur  under  the  influence  of  chemical 
stimuli,  which,  inter  alia,  go  hand  in  hand  with  negativity  of 
the  points  in  question. 

II. — The  Current  of  Action 

A  complete  account  of  the  earlier  theories  of  electrical 
activity  in  muscular  contraction  would  here  be  out  of  place 
since,  like  the  history  of  the  "  current  of  rest "  in  muscle,  the 
subject  has  been  thoroughly  reviewed  by  du  Bois-Eeymond, 
in  Part   II.  of  the  "  Untersuchungcn."      It  is   enough    to   recall 


360  ELECTRO-PHYSIOLOGY 


the  fact  that  an  electrical  theory  of  muscular  contraction  was 
founded  by  Prevost  upon  certain  observations  of  Ampere,  as 
early  as  1837,  and  this  is  of  interest,  inasmuch  as  it  shows 
to  what  extent  physiological  conceptions  may  be  influenced 
by  current  physical  theories.  Prevost  convinced  himself  by 
microscopic  investigation  that  the  cross-striation  of  the  fibres 
of  skeletal  muscle  was  simply  the  optical  expression  of  looped 
nerve-endings  lying  parallel  with  one  another,  which  pull  in 
opposite  ways  at  the  moment  when  an  electrical  current 
traverses  the  entire  system  of  loops  in  the  same  direction.  In 
order  to  demonstrate  this  current,  Prevost  introduced  a  "  very 
fine  non-magnetic  needle  into  the  frog's  leg  in  the  direction  of 
the  fibres ;  the  point  projected,  and  was  covered  with  iron- 
filings  " ;  at  the  moment  at  which  a  vigorous  contraction  was 
produced  by  injury  to  the  spinal  cord,  the  iron  -  filings  were 
said  to  arrange  themselves  round  the  point  of  the  needle,  as  if 
they  had  been  magnetised.  A  similar  theory  was  advanced  by 
"Wharton  Jones  in  1844  (du  Bois,  I.e.  p.  10).  "According  to 
his  view,  which  follows  on  with  Bowman's  observations  (com- 
position of  muscle-fibres  out  of  '  discs '),  the  muscle-fibres  consist 
of  discs  arranged  in  columns,  or  rouleaux,  connected  by  a  flexible 
and  elastic  substance,  which  enable  them  to  approximate,  or 
recede  from  one  another.  The  discs,  according  to  Wharton 
Jones,  are  converted  by  the  influence  of  the  nerve  into  electro- 
magnets, and  their  antagonistic  traction  produces  the  shortening 
of  the  muscle.  The  electro -magnets  ("  appareils  nervo-mag- 
n^tiques  ")  are  not  indeed  surrounded  on  all  sides  by  nerves,  as 
an  iron  magnet  would  be  with  copper  wire ;  this  only  proves, 
however,  that  nature  adapts  itself  to  simpler  arrangements. 
The  first  real  advance  in  this  department  is  once  more  owing  to 
that  indefatigable  worker  who  discovered  the  muscle  current 
almost  simultaneously  with  du  Bois  -  Eeymond.  C.  Matteucci, 
after  taking  infinite  pains,  from  1838,  to  demonstrate  electrical 
action  during  muscular  activity,  and  repeating  inter  alia  the 
experiments  of  Prevost  in  different  forms,  succeeded  at  last 
in  discovering  a  fact  which  gave  the  required  determination. 
On  February  28,  1842,  Matteucci  communicated  to  the  Paris 
Academy  the  account  of  an  experiment  which  must  be  reckoned 
among  the  most  elegant  and  interesting  in  experimental  physio- 
logy.      This  was   proof  of  what    du'  Bois -Eeymond    afterwards 


IV  ,.  ELECTROMOTIVE  ACTION  IN  MUSCLE  361 

termed  "  secondary  contraction,"  in  whicli  the  leg  of  a  frog 
twitches  vigorously  when  its  nerve  is  laid  upon  the  muscle  of 
an  excited  second  leg.  In  the  same  year  Matteucci  received 
the  prize  for  experimental  physiology  from  a  Committee  of  the 
Academy,  which  included  the  older  Beqnerel,  and  the  renowned 
physicist  concluded  from  the  experiment,  which  was  recognised 
as  valid  on  all  sides,  "  that  an  electrical  discharge  must  take 
place  in  the  muscle  at  the  moment  of  contraction,  and  finds 
its  way  in  part  through  the  nerves  of  the  second  frog." 
Matteucci  had  previously  observed  that  the  secondary  contrac- 
tion was  not  obstructed  by  moist  filter-paper,  while  on  the  other 
hand  it  was  stopped  by  gold  plates  or  non-conductors,  laid 
between  the  nerve  of  the  secondary  preparation  and  the  muscle 
of  the  primary.  These  results  are  in  complete  agreement  with 
the  theory  as  stated.  Matteucci,  on  his  side,  was  eager  to  find 
new  proofs  of  the  presumptive  development  of  electricity  in 
contraction — compared  directly  by  Bequerel  with  the  stroke  of 
the  torpedo.  As  early  as  1845,  a  new  publication  appeared  in 
English  on  the  "  induced  contraction,"  as  it  was  now  termed  by 
Matteucci.  He  had  found  its  appearance  to  be  independent  of 
the  position  of  the  secondary  nerve  on  the  muscle  of  the  primary 
preparation ;  it  may  be  laid  parallel  with  the  fibres,  or  across 
them,  or  in  any  direction ;  the  secondary  contraction  invariably 
follows.  Matteucci  cut  a  disc  of  muscle  out  of  the  leg  with  a 
razor ;  the  secondary  contraction  never  failed,  provided  the  test- 
ing nerve  was  in  contact  with  the  cut  surface.  He  further 
obtained  twitches  of  the  third  and  fourth  order  by  placing  the 
nerve  of  a  second  test-preparation  upon  the  gastrocnemius  of  the 
first,  the  nerve  of  a  third  preparation  on  the  muscle  of  the 
second,  and  then  exciting  the  primary  nerve.  With  regard  to 
the  presumably  electrical  nature  of  the  secondary  twitch, 
Matteucci  moistened  the  surface  of  the  first  muscle  with  different 
conducting  and  non-conducting  fluids,  e.g.  serum,  blood,  oil,  and 
dilute  alcohol,  varnish,  oil  of  turpentine,  etc.,  in  which  the 
nerve  of  the  second  preparation  was  bedded.  In  none  of  these 
did  Matteucci  find  the  twitch  abolished,  although  this  happened 
with  the  thinnest  plates  of  a  firm  body,  e.g.  glass,  talc,  etc.  The 
skin  of  the  frog,  like  filter-paper,  was  favourable  to  secondary 
contraction.  These  last  observations  misled  Matteucci  in  regard 
to    the   prevailing   theory  of  the  electrical    origin  of  secondary 


362  ELECTRO-PHYSIOLOGY  chap. 

contraction,  and  he  believed  himself  to  have  discovered  a  special 
force,  manifesting  itself  by  action  at  a  distance,  which  proceeds 
from  the  muscle  at  the  moment  of  contraction ;  this  led  him 
to  give  the  name  of  "  induced  twitch "  to  the  phenomenon  he 
had  discovered. 

Up  to  this  point  Matteucci  had  no  knowledge  of  a 
discovery  made  by  du  Bois-Eeymond  in  1842,  in  following 
up  an  older  investigation  of  the  Italian  experimenter.  As  far 
back  as  1838,  Matteucci  had  discovered  that  the  ascending 
current  in  the  frog  ("  courant  propre ") — as  demonstrated  by 
Nobili  in  1827  with  Schweigger's  multiplier  on  galvanic  pre- 
parations, and  referred  by  du  Bois  to  the  current  of  the  single 
muscle — disappeared  altogether,  or  was  much  weakened  during 
tetanus  (later,  he  believed  himself  convinced  of  the  contrary). 
Du  Bois-Eeymond,  who  had  meantime  formulated  the  "law 
of  the  muscle  current,"  went  on  to  ask,  How  the  muscle 
current  behaved  during  persistent  excitation  ?  The  first  com- 
munication of  the  weighty  results  of  this  inquiry  appeared  in 
1842,  in  a  "preliminary  sketch."  In  this  it  was  shown  that 
the  longitudinal  transverse  current  of  the  gastrocnemius  did  not 
disappear  during  contraction,  when  the  nerve  was  tetanised,  but 
that  it  did  diminish  perceptibly  in  intensity. 

The  capital  experiment  of  this  investigation  was  originally 
arranged  as  follows  (Fig.  112).  The  gastrocnemius  lies  with 
its  longitudinal  and  artificial  (or  corroded  natural)  transverse 
sections  upon  the  pads  of  the  leading-in  dishes ;  the  central  end 
of  the  nerve  is  stretched  over  platinum  electrodes,  connected  with 
the  tetanising  apparatus.  The  experiment  invariably  results 
in  an  unmistakable  diminution  of  the  muscle  current  during 
tetanus,  a  negative  variation,  as  seen  in  the  backward  swing 
of  the  needle  of  the  multiplier,  or  circular  magnet  of  the 
galvanometer.  All  possible  objections  and  sources  of  fallacy 
were  investigated  by  du  Bois-Eeymond  with  his  usual  thorough- 
ness, and  he  succeeded  in  establishing  beyond  doubt  that  a 
diminution  of  E.M.F.  does  actually  accompany  the  state  of  excita- 
tion. In  later  experiments  du  Bois  investigated  the  negative 
variation,  with  similar  results,  on  the  regular  parallel -fibred 
muscles  of  the  thigh,  instead  of  the  complicated  gastrocnemius, 
change  of  form  in  the  muscle  being  avoided  by  tension  between 
two    fixed   points.      The   method  of  compensating  the  "  current 


elp:ctromotive  action  in  muscle 


363 


of  rest  "  as  introduced  by  du  Bois,  has  the  distinct  recommendation 
that  it  shows  the  negative  variation  to  be  a  deflection  contrary 
in  direction  to  the  original  effect,  its  distribution  in  time,  which 
is  accelerated  at  first  with  an  aperiodic  magnet,  becoming  gradually 
slower.  On  prolonging  the  excitation  there  is  a  slow  return  to 
the  position  of  rest,  which  is  sometimes  reached  during  the  closure 
of  the  circuit,  in  other  cases  only  after  it  has  been  opened  again ; 
but  the  return  is  seldom  perfect.       There  is  usually  a  permanent 


diminution  of  the  muscle  current  (negative  after-effect),  the  degree 
of  which  depends  on  the  strength  of  the  previous  excitation. 

The  immediate  inference  as  to  the  meaning  of  the  backward 
swing  of  the  magnet  during  tetanus  would  be,  that  there  was 
a  ^;crs?'s«!eM;!  diminution  of  the  longitudinal  current,  continu- 
ous throughout  the  period  of  excitation.  In  view,  therefore, 
of  the  known  properties  of  the  physiological  rheoscope,  which 
reacts  mainly  at  the  rise  or  disappearance,  or  sudden  variations 
in  density  of  a  current,  it  might  be  expected  that  the  leg  serving 


364  ELECTRO-PHYSIOLOGY 


to  test  the  current  would  contract  in  consequence  of  the  rapid 
decrease  in  current  at  the  beginning  of  tetanus,  if  the  nerve 
bridged  over  the  longitudinal  and  transverse  sections  of  the  excited 
muscle.  On  the  other  hand,  we  should  hardly  look  for  this  result 
at  the  end  of  tetanus,  since  the  muscle  only  returns  gradually  to 
its  original  condition.  This  experiment,  as  tried  by  du  Bois- 
Eeymond,  yielded  a  very  striking  result,  not  at  all  in  correspond- 
ence with  what  was  anticipated.  The  test-limb,  i.e.,  not  merely 
twitched  at  the  beginning  of  tetanus,  but  actually  fell  into  secondary 
tetanus  during  the  whole  of  the  primary  excitation.  If  this  is  im- 
perfect, so  that  each  single  twitch  remains  recognisable,  and  the 
muscle  is  then  connected  on  the  one  hand  with  the  galvanometer, 
and  on  the  other  with  the  physiological  rheoscope,  the  latter 
responds  by  a  secondary  twitch  to  every  primary  contraction,  while 
the  magnet,  in  consequence  of  its  sluggishness,  swings  back  simply 
in  the  direction  of  the  negative  variation.  We  may,  therefore, 
and  indeed  must  suppose  that  even  with  the  most  complete 
fusion  of  the  visible  contractions  of  the  primary  muscle,  into  sus- 
tained tetanus,  each  impact  of  stimulation  calls  out  an  excessively 
short  negative  variation,  distinct  in  time  from  that  which  succeeds 
it,  so  that  the  muscle  current  fluctuates,  as  it  were,  up  and  down 
in  the  rhythm  of  the  tetanising  stimulus,  by  which  we  see  that 
notwithstanding  the  apparently  steady  contraction  of  the  muscle 
in  tetanus,  it  really  originates  in  discontinuous  alterations  of 
state,  exhibited  more  especially  in  its  galvanometric  response 
as  above.  The  extraordinary  superiority  of  the  physiological 
rheoscope  to  all  other  known  physical  apparatus  for  testing 
current  is  obvious,  and  it  is  only  quite  recently  that  a  method 
has  been  discovered  which  (with  regard  to  the  possibility  of 
demonstrating  variations  in  current  lasting  for  a  short  period 
only,  and  following  in  rapid  succession)  may  be  compared  with 
the  faithful  response  of  the  physiological  rheoscope  to  the 
electrical  fluctuations.  The  accompanying  diagram  (Fig.  113) 
gives  a  clear  picture  of  the  behaviour  of  the  muscle  current  in 
tetanus  as  attested  from  observations  on  secondary  tetanus. 

"  If  the  abscissa  (o,  t)  represents  the  time,  on  which  the  ampli- 
tude of  the  current  is  drawn  at  each  second  as  ordinate,  (o,  ct) 
further  represents  the  constant  magnitude  of  the  muscle  current 
in  the  state  of  rest ;  for,  in  order  merely  to  produce  a  diminutional 
effect  in  the  multiplier,  it  is  indifferent  whether  (o,  a)  becomes 


ELECTROMOTIVE  ACTION  IX  MUSCLE 


■365 


persistently  smaller,  as  in  (h,  p,  g),  or  whether  this  occurs  spasmodic- 
ally, so  that  the  current  may  sink  much  deeper,  and  even  below  the 
axis  of  the  abscissa  (which  indicates  reversed  direction  of  current). 
The  effect  upon  the  galvanometer  is  the  same  in  both  cases.  In 
the  physiological  rheoscope  it  is  quite  different.  The  form  of  the 
curve  (h,  'jp,  g)  would  never  produce  tetanus  in  the  test-limb ;  we 
are  reduced  to  the  assumption  that  it  is  the  jagged  curve,  though 
with  constant  (unknown)  depth  of  declinations,  which  really 
occurs  in  tetanus"  (du  Bois-Eeymond).  In  order  to  deal 
fairly  with  the  actual  circumstances,  it  must  also  be  noticed 
that  each  individual  elementary  curve  of  variation  fails,  in  con- 
sequence of  the  after-effect,  to  reach  the  height  of  the  original 
ordinate,  so  that  the  base-points 
of  the  single  curves  fonn  a 
descending  staircase,  as  in 
Fig.  113.  Supported  by  these 
facts  and  hypotheses,  du  Bois- 
Eeymond  believed  himself  justi- 
fied in  propounding  a  general 
theory  of  Matteucci's  second- 
ary contraction,  representing  it 
simply,  i.e.  as  the  pliysiological 
ej^ect  of  the  negative  variation 
of  the  muscle  current  present 
in  every  single  twitch,  and  only 
marked  by  the  sluggishness  of 
the  magnet.  (It  is  to  be  noted  that  the  modern  galvanometers 
with  light,  aperiodic  magnets  present  no  such  difficulty,  and 
the  demonstration  is  as  certain  as  in  the  physiological  rheo- 
scope). According  to  this  view,  du  Bois  held  it  to  be  a 
necessary  condition  for  the  appearance  of  the  secondary  twitch, 
that  the  nerve  of  the  secondary  preparation  should  occupy  a 
definite  position  upon  the  primary  muscle.  According  to  his 
first  results,  the  secondary  contraction  only  appears  regularly 
"  when  the  nerve  closes  the  circuit  between  the  two  dissimilar 
surfaces  of  the  muscle  (longitudinal  and  transverse  section)." 
Matteucci  had  meantime  found  the  appearance  of  the  secondary 
contraction  to  be  fairly  independent  of  the  position  of  the  nerve 
upon  the  primary  preparation,  and  had  even  placed  it  so  that 
it  formed  a  loop  round  the  twitching  muscle.      It  is,  in  fact,  very 


Fig.  113. — Negative  variation  in  tetanus. 
(Hermann.) 


366  ELECTRO-PHYSIOLOGY 


easy  to  prove  that  the  secondary  contraction  is  by  no  means 
invariably  due  to  negative  variation  of  a  pre-existing  current, 
as  was  admitted  later  by  du  Bois-Reymond  himself,  when  he  in- 
vestigated the  negative  variation  of  "  parelectronomic  "  muscle. 

Before  pursuing  this  point  any  further  we  must,  however, 
attack  another  question,  which  was  left  in  abeyance  in  an 
earlier  connection.  It  was  stated  that  appearance  of  secondary 
tetanus  might  be  taken  as  a  proof  that  the  muscle  current 
undergoes  no  continuous  diminution  during  contraction,  but  that 
during  that  time  it  is  constantly  varying  backwards  and  forwards, 
although  these  movements  are  not  followed  by  the  magnet,  on 
account  of  its  sluggish  reaction.  The  rheoscopic  limb  of  the  frog, 
however,  leaves  us  in  doubt  as  to  hoM''  nearly  the  summits  of  the 
single  curves  of  variation  approximate  to-  the  zero  line  (indicated 
by  dots  in  Fig.  113) — whether  they  do  reach  it,  so  that  the 
current  is  nil  at  the  moment  of  contraction — or  finally  exceed  it, 
which  corresponds  with  a  reversal  of  current. 

Du  Bois-Eeymond  himself  attempted  to  solve  the  first 
question  (Untcrsuchungcn,  ii.  p.  120),  and  with  this  object  con- 
structed apparatus  "  by  which  the  muscle  could  be  submitted  to  a 
rapid  series  of  excitations  through  its  nerve,  moment  by  moment, 
in  rapid  succession.  After  each  moment  of  excitation,  the  muscle 
current  could  be  closed  for  a  brief  period,  and  this  closure  might 
follow  at  a  given  time  between  any  two  stimuli.  If  the  muscle 
current  therefore  sinks  between  any  two  stimuli  during  tetanus 
in  a  normal  curve,  and  then  rises  again,  its  deepest  point  will  be 
reached  so  soon  as  the  closure  of  the  muscle  current  coincides  in 
position  with  this  point."  The  problem  is  still  better  expressed 
in  the  accompanying  diagram  (Fig.  114). 

Let  the  abscissa  {0,  T)  represent  the  time,  on  which  are 
drawn  the  ordinates,  i.e.  height  of  the  muscle  current  (h),  so  that 
the  line  (»^,  m),  etc.,  corresponds  with  the  line  of  the  current 
during  rest.  In  the  equidistant  moments  of  time  (t,  t^,  f,  f), 
etc.,  there  is  always  an  excitation  of  the  muscle,  which  re- 
sults in  a  negative  variation  of  the  existing  "  current  of  rest," 
and  its  course,  as  will  be  shown,  represents  the  curve  (m,  o,  m), 
between  each  two  stimuli.  The  true  form  of  the  latter  is 
easily  determined  if  the  galvanometer  circuit  is  closed  between 
every  two  excitations,  for  a  moment  only  {T),  at  periodically 
repeated    and    uniform    intervals    {t^,    f',    f,   etc.)        The    same 


ELECTROMOTIVE  ACTION  IN  MUSCLE 


367 


segment  (the  hatched  part  of  the  curve,  Kg.  114)  is  therefore 
always  cut  out  of  the  superficies  of  a  variation  curve,  and 
through  its  summation  a  deflection  of  definite  proportions  is 
produced.  And,  since  the  time  of  galvanometer  closure  can  be 
prolonged  as  required  over  the  entire  interval  between  the  two 
stimuli,  the  form  and  magnitude  of  the  curve  of  variation  corre- 
sponding to  each  single  stimulus  are  easily  determined.  The 
credit  of  having  constructed  apparatus  that  satisfied  these  require- 
ments belongs  to  Bernstein  (20),  whose  "differential  rheotome  " 
has  since  found  an  extended  application  in  experimental  physio- 
logy.    The  instrument  consists  essentially  of  a  wheel  (r)  (Fig.  115) 


Fig.  114. 


revolving  easily  round  the  central  axis,  worked  as  uniformly  as 
possible  (5-10  revolutions  per  second)  by  clockwork,  or  a  small 
motor.  At  the  periphery  of  the  wheel  there  are  three  isolated 
metal-points  (according  to  Hermann,  brushes  of  copper- wire),  one  of 
which  (c)  forms  the  exciting  contact,  the  other  two  {c',  c')  effect  the 
closure  of  the  galvanometer  circuit.  The  former  slides  at  each 
revolution  over  a  thin  extended  wire,  or  pool  of  mercury,  and 
thus  closes  the  circuit  {B',  R")  of  the  primary  coil  of  an  induction 
apparatus.  The  currents  produced  in  rapid  succession  in  the 
secondary  coil  (make  and  break  shock)  are  led  into  the  prepara- 
tion, and  may  be  regarded  collectively  as  a  momentary  stimulus. 
Diametrically  opposite  to  the  exciting  contacts,  isolated  from  the 


368 


ELECTRO-PHYSIOLOGY 


metal  wheel,  but  in  circuit  with  one  another,  are  the  two  points 
(brushes)  forming  closure  of  the  galvanometer,  which  at  a  certain, 
point  of  the  revolution  pass  through  the  mercury  pools  of  two 
isolated  steel  cups  (g^,  (f),  or  over  amalgamated  copper  contacts 
included  in  the  galvanometer  circuit  {B^,  B.^.  The  pools  (contacts) 
are  movable,  so  that  the  duration  of  the  simultaneous  dip, 
i.e.  duration  of  galvanometer  closure  {T),  can  be  altered  within 
a  wide  margin.  Now,  instead  of  extending  this  interval  over  the 
surface  of  the  curve  of  variation  as  above,  the  distance  of 
the  time  {T)  from  the  moment  of  excitation  {t,  t^),  etc.,  is 
regulated  in  Bernstein's  instrument  by  alteration  of  the  slider 


Fig.  115. ^Bernstein's  difterential  rheotome  (seen  from  above). 


which  carries  the  exciting  contact.  The  whole  arrange- 
ment of  the  experiment  resembles  the  diagram  (Fig.  116). 
Owing  to  the  complicated  structure  of  the  gastrocnemius,  the 
sartorius  is  better  adapted  for  the  study  of  the  negative  variation, 
its  demarcation  current  being  compensated  to  start  with.  In 
consequence  the  galvanometer  magnet  remains  at  rest  during 
rotation,  and  is  only  deflected  when  there  is  an  alteration  of  the 
muscle  current  during  the  time  (T).  If  the  slider  is  then 
arranged,  as  in  Fig.  116,  so  that  the  closure  of  the  circuit 
of  the  primary  coil  occurs  at  the  same  moment  at  which 
the  galvanometer  circuit  is  broken  by  the  two  contacts,  a 
complete   revolution    occurs   before    the    closure   of    the    muscle 


ELECTROMOTIVE  ACTION  IN  MUSCLE 


369 


circuit  repeats  itself,  and  if  the  process  of  negative  closure  has 
run  out  during  this  period,  no  deflection  will  be  obtained.  On 
actually  working  the  experiment,  however,  we  still  find  a 
negative  deflection  increasing  slowly  throughout  the  entire  period 
of  excitation,  i.e.  in  the  direction  of  the  compensating  current,  due 
apparently  to  the  diminutional  after-effect  of  excitation  upon  the 
muscle  current  as  described.  Now,  if  the  exciting  slider  is 
brought  more  forward,  so  that  excitation  occurs  while  the 
galvanometer  contacts  are  still   dipping   into   mercury,  we  find 


Fig.  116  — Schema  of  rheotome  experiment.    (Bernstein.) 


at  a  particular  point  a  sudden  incre77ient  in  the  deflection,  which 
increases  rapidly  in  the  negative  direction  on  pushing  on  the 
slider,  and  finally  reaches  a  maximum,  after  which  it  decreases 
again  with  further  displacement  of  the  slider,  and  at  last  remains 
persistently  lower  than  it  was  at  the  beginning  of  the  excitation. 
This  shows  that  there  is  a  measurable  interval  between  the 
moment  of  excitation  at  one  point  of  a  muscle  with  parallel 
fibres  (Bernstein  always  chooses  the  lower  end  of  the  sartorius 
as  being  free  from  nerves),  and  the  beginning  of  the  negative 
variation  at  the  other,  provided  with  an  artificial  cross-section ; 

2  B 


370  ELECTRO-PHYSIOLOGY 


also  that  the  negative  variation  in  the  tract  of  muscle  led  off, 
itself  has  a  certain  duration.      For  on  pushing  the  slider  along,  the 
deflections  increase  to  a  maximum,  at  which  they  persist  for  some 
time ;    but  if  it  is  pushed  still  further  forward,  no  adjustment 
will  produce   a   deflection  of  the   magnet.      The  slider  may  be 
pushed  over  the  whole  graduated  circle,  without  any  repetition  of 
the  galvanometer  deflection,  until  it  has  passed  back  beyond  its 
first  position,  and  reaches  that  in  which  the  first  negative  deflec- 
tion became   apparent.      The  experiment  therefore  confirms  the 
conclusions  derived  from  the  observation  of  secondary  tetanus, 
to  the  effect  that  the  negative  variation  of  the  muscle  current 
on    tetanising   corresponds   not    to    a    continuous   diminution   of 
P.D.   between  longitudinal  and   cross -section,   but   to   a  discon- 
tinuous  waxing   and  waning  in   the   rhythm  of  the  excitation. 
We  see  further  that  each  single  negative  variation  comes  into 
existence  more  rapidly  than  it  vanishes  ;  graphically  expressed, 
its  curve   rises  steeply  to  a  maximum,  and  then  sinks    slowly 
down    again    (cf.    Fig.    114).       If    the    rate    of    revolution    of 
the    rheotome    wheel,    and    the    distance    expressed    in    degrees 
between  the  original  position  of  the  slider  (when  simultaneously 
excited    and    led    off),   and   that    at    which   the   first    deflection 
occurs,  is   known,  it  is    easy    to   calculate  the   time    (relatively 
to  the  length  of  muscle  between  the  point  of  stimulation  and  the 
leading-off  contact  on  the  longitudinal  surface)  required  by  the 
process  of  negative  variation,  in  order  to  transmit  itself  from  the 
seat  of  excitation  to  the  leading-off  longitudinal  contact.      So  too 
the  duration  of  the  negative  variation  may  be  calculated  from  the 
distance  of  the  initial  and  final  positions  of  the  slider,  and  the 
revolutions  of  the  wheeL      We  should  expect  the  duration  of  the 
negative    variation   to   increase   with   the    distance   between   the 
leading-off  contacts,  and  this  obviously  corresponds  with  a  certain 
time -interval,  which   must    be   less   in   proportion   as   the  tract 
between   the  electrodes  is  shortened.       But  this  anticipation  is 
not   confirmed   in   experiment.       The    duration   of  the   negative 
variation  is  approximately  equal,  whatever  the  distance  of  the  con- 
tacts.     This,  however,  means  that  the  process  which  effects  the 
backward  swing  of  the  magnet  is  demonstrated  by  the  galvano- 
meter only  while  it  passes  over  the  base  points  of  the  leading-off' 
circuit  in  contact  with  the  longitudinal  surface,  and  not  beyond 
these  points.      Bernstein  gives  the  velocity  of  the  negative  varia- 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  371 

tion  at  an  average  of  2'927  metres  per  sec.  Its  duration  is  ^-^ 
to  3I0  sec. 

With  the  aid  of  this  repeating  method  it  is  possible  to 
decide  the  magnitude  of  the  negative  variation,  and  to  determine 
whether  at  the  moment  when  the  curve  of  variation  reaches 
its  maximum,  the  current  led  off  will  sink  to  zero,  or  become 
reversed  in  direction.  For  this  purpose  the  two  mercury  dishes 
are  so  arranged  that  the  closure  of  the  galvanometer  circuit  {T) 
is  made  as  short  as  possible.  Moreover,  in  experimenting,  the 
slider  must  be  placed  in  such  a  position  that  the  closure  of  the 
galvanometer  coincides  after  each  stimulus  with  the  maximum  of 
the  subsequent  negative  variation.  When  this  is  done,  compensa- 
tion may  be  shut  off,  and  the  first  deflection  on  the  galvanometer 
measured,  as  produced  by  the  current  in  the  non-excited  muscle 
during  the  revolution  of  the  rheotome  wheel.  Now,  if  the  magni- 
tude of  the  effect  is  determined  during  tetanus  at  the  same 
rate  of  revolution,  it  will  obviously  depend  on  the  difference  in 
strength  between  "  resting  "  muscle  current  and  negative  variation, 
in  the  interval  under  observation.  The  direction  of  the  effect 
shows  immediately  which  current  is  the  strongest.  If  the  current 
is  reversed  at  the  moment  of  the  negative  variation,  i.e.  at  the  time 
when  it  is  at  its  maximum,  the  scale  must  turn  in  the  negative 
direction.  Bernstein,  however,  never  found  a  negative  deflection  ; 
the  effect  was  always  positive,  although,  as  we  should  expect,  it 
was  much  weaker  than  the  corresponding  deflection  produced  by 
the  current  in  the  resting  muscle.  As  a  rule,  therefore,  the 
curve  of  variation  does  not  sink  to  zero. 

The  graphic  record  of  these  results  is  a  great  assistance 
towards  understanding  them,  as  was  indeed  anticipated  in  ex- 
plaining the  principle  of  the  rheotome.  Let  {t,  t')  (Fig.  117) 
be  the  time  abscissa,  also  two  consecutive  moments  of  stimu- 
lation, {h)  the  height  of  the  resting  muscle  current,  {T)  the  time 
of  the  galvanometer  closure,  supposed  to  be  movable  between 
{t)  and  {t').  If  this  occurs  in  {T')  there  will  be  no  perceptible 
deflection,  which  first  begins  when  the  galvanometer  closure  occurs 
at  T' ;  from  that  point  the  negative  deflection  decreases  rapidly 
in  magnitude  with  further  alteration  of  the  time  of  closure,  and 
finally  dies  out  (slowly),  so  that  a  curve  is  produced  which  falls 
steeply,  and  rises  up  again  slowly,  without,  however  (in  the  after- 
effect), recovering  its  original  height.      The  deepest  point  of  this 


372 


ELECTRO-PHYSIOLOGY 


curve  does  not  usually  reach  the  abscissa  (the  muscle  current  is 
not  abolished).  The  length  {r,  m)  corresponds  obviously  to  the 
period  between  the  moment  of  excitation  and  the  instant  at  which 
the  process  of  the  negative  variation  arrives  at  the  first  leading- 
off  electrode,  while  the  time  represented  by  the  line  (m,  o)  corre- 
sponds with  the  period  of  the  negative  variation.  In  order  to 
conceive  the  true  process  graphically,  the  figures  must  be  imagined 
one  behind  the  other  many  times  over.  While  the  stimuli  follow 
at  equal  intervals  (t,  t^,  f,  etc.),  the  closure  period  (T)  is 
always  at  the  same  distance  from  the  corresponding  moment  of 
excitation ;  the  effect  on  the  galvanometer  will  then  be  zero. 
But  if  the  closure  of  the  galvanometer  coincides  with  the  beginning 
of  the  negative  variation,  the  same  impact  will  be  repeated  at 


Fig.  117. — Schema  of  rheotome  experiment.    (Bernstein.) 


each  revolution,  with  a  common  effect  on  the  magnet.  This 
obviously  resembles  "  that  of  a  constant  current,  equal  in  height 
to  the  superficial  content  of  all  parts  of  the  curves  above  (T), 
divided  by  the  time  of  observation."  It  is  possible  in  this  way 
to  constru.ct  the  whole  curve  of  variation  from  consecutive 
observations,  and  this  has  till  now,  at  all  events  for  striated 
muscle,  been  the  sole  means  of  determining  its  form  and  process. 
This  would  otherwise  have  been  impossible  without  applying 
the  method  of  summation  (repetition),  since  even  the  most 
suitable  instruments,  e.g.  the  capillary  electrometer,  are  incapable 
of  adequately  demonstrating  the  negative  variation  which  corre- 
sponds with  a  single  excitation.  It  is  easy,  on  an  aperiodic 
galvanometer  with  a  very  free  magnet,  to  obtain  a  deflection 
from    the     negative    variation    that    accompanies    each     single 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  373 

twitch,  but  the  time  which  such  a  deflection  occupies  corre- 
sponds much  less  closely  with  the  time  of  the  variation  of 
current,  than  the  movement  of  the  capillary  electrometer 
(which  for  the  rest  is  far  too  insensitive  for  the  object  before 
us).  Nevertheless,  the  construction  of  the  curve  of  varia- 
tion by  a  direct  record  is  eminently  desirable.  Since  it  does 
not  appear  possible  to  overcome  the  sluggishness  of  the  magnet, 
and  to  raise  its  mobility  so  far  as  to  enable  it  to  follow 
the  quicker  variations  of  the  current  faithfully,  Hermann  has 
recently  tried  the  reverse  method,  by  attempting  to  retard  the 
galvanic  process  under  observation  as  much  as  possible  (21). 
He  accomplished  this  by  the  simple  and  ingenious  method  of 
turning  the  two  copper  knobs,  which  effect  contact  with  the 
galvanometer,  and  are  attached  to  an  ebonite  disc,  in  the  same 
direction  as  the  wheel  of  the  Bernstein  rheotome  during 
its  revolution,  only  much  more  slowly.  It  is  obvious  that  the 
interval  between  stimulus  and  galvanometer  closure  would  thus 
be  constantly  altered,  so  that  the  whole  process  of  the  negative 
variation  may  be  read  off  at  a  given  reduction  of  time  upon 
the  galvanometer.  The  magnet  would  then  follow  the  time- 
relations  of  the  electrical  change  with  complete  fidelity,  and 
it  would  only  be  necessary  to  transfer  its  movements  by  means  of 
a  ray  of  light  reflected  from  the  mirror  on  to  a  moving  sensitive 
surface,  in  order  to  obtain  a  true  photographic  record  of  the  curve 
of  variation.  It  is  superfluous  to  say  that  the  results  obtained 
by  this  method  ("  rheotachygraphy  ")  coincide  with  the  conclusions 
of  the  ordinary  rheotome  experiments. 

The  "  variation  curve "  therefore  corresponds  with  the 
development  and  time-relations  of  the  negative  variation  in  a 
definite  part  of  the  muscle,  i.e.  the  point  of  the  longitudinal 
section  from  which  it  is  led  off.  But  since  the  changes  funda- 
mental to  it,  which  are  unequivocally  in  direct  ratio  with  the 
excitatory  process,  proceed  2Mri  passic  with  the  rapidity  at  which 
excitation  is  propagated  from  section  to  section,  it  is  legitimate  to 
inquire  in  what  length  of  muscle  the  single  points  are  found  after 
excitation  to  be  simultaneously  at  different  phases  of  negative 
variation.  And  thus  we  come  to  Bernstein's  original  proposition 
of  the  "  excitatory  tvave  "  in  muscle.  "  A  muscle  fibre  (M,  M)  (Fig. 
118)  is  led  off  from  its  artificial  cross-section  {q)  and  from  the 
surface  of  the  elements  {d,  M{),  which  is  hypothetically  marked 


374 


ELECTRO-PHYSIOLOGY 


off  by  two  cross-sections  in  close  juxtaposition.  If  the  fibres 
in  {p)  are  excited  by  momentary  closure,  the  negative  variation, 
after  a  given  period,  reaches  the  element  (d,  M-^)  at  the  very 
moment  at  which  the  first  signs  of  the  negative  variation 
appear  in  the  galvanometer  circuit.  At  the  same  moment, 
however,  the  negative  variation  reaches  its  maximum  in  the 
element  (^d,  M^)  nearer  to  the  point  of  excitation,  while  it  has 
already  subsided  at  (d,  M^,  a  third  element. 

"  If  the  magnitudes  of  the  negative  variation  are  drawn  as 
ordinates  over  these  and  the  intermediate  elements  of  the  muscle- 
fibre,  we  obtain  the  curve  {m,  n,  o),  which  represents  the  state  of 
electromotive  change  in  the  subjacent  elements  of  the  muscle 
fibre."  Bernstein  designates  the  curve  (m,  n,  6)  the  "  wave  of 
excitation."       It    spreads    like    an    undulation    from    the     spot 


/ 

n 

\ 

oy 

MV. 

. 

■ 

"" 

p 

d 

il 

/. 

d 

J 

L       c 

7M, 

Fig.  118. — Schema  of  tlie  "excitatory  wave."    (Bernstein.) 

excited  over  the  muscle  fibre,  in  either  direction,  producing 
successively  in  each  element  of  the  fibre  the  complete  process  of 
the  negative  variation,  so  that  the  wave  advances  at  its  own 
length  as  long  as  the  negative  variation  continues.  Bernstein 
calculates  the  length  of  the  wave  at  an  average  of  10  mm.,  from 
his  observations. 

If  we  sum  up  the  results  of  all  these  experiments  and 
discussions  on  the  negative  variation  in  a  parallel-fibred  muscle, 
provided  with  an  artificial  cross-section,  it  may  be  concluded 
that,  if  one  end  of  the  muscle  is  excited  by  single  induction- 
shocks,  while  leading  off  from  the  other,  a  change  is  initiated 
in  the  first  segment  concerned  at  a  given  interval  after  each 
single  stimulus,  which  interval  corresponds  with  the  distance 
between  the  leading-oif  longitudinal  contact  and  the  point  of 
excitation.      The  change  set  up  gradually  increases,  reaches  its 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  375 

maximum  at  a  certain  moment,  and  is  finally  quelled  again. 
These  phases  are  expressed  in  the  gradual  reduction  of  difference 
in  electrical  potential  between  the  two  leading-off  contacts  in 
the  muscle.  Since  we  know  that  the  artificial  transverse 
section  of  the  muscle  is  electrically  negative  towards  each  point 
of  the  uninjured  surface,  all  these  phenomena  can  easily  be 
explained  by  postulating  that  the  change  in  the  excitable  stcbstance 
'propagated  frovi  the  point  of  excitation  through  the  muscle-fibres 
is  associated  with  negativity  of  the  latter.  We  shall  subsequently 
find  direct  proof  of  this  dictum.  For  the  moment  it  may  be 
accepted  as  a  hypothesis,  which  elucidates  the  foregoing  observa- 
tions. We  assume,  therefore,  that  at  the  moment  at  which  a 
short  stimulus  (momentary  excitation)  takes  effect  upon  any  point 
of  the  fibre,  a  chemical  alteration  is  developed  at  the  same  point, 
expressed  by  negativity  of  this  part  of  the  fibre  towards  adjacent, 
non-excited  parts.  Stress  must  be  laid  on  the  fact,  as  attested 
by  every  experiment,  that  this  change  (which  must  be  regarded 
as  identical  with  the  excitatory  process)  begins  directly  at  the 
moment  of  excitation,  i.e.  without  any  perceptible  latent  period, 
rapidly  reaches  a  maximum,  and  then  declines  again  slowly. 
The  succession  of  the  different  stages  of  this  change  at  the  same 
point  of  the  fibre,  whether  directly  or  indirectly  excited,  may  be 
represented  in  a  curve,  designated  above  the  "  curve  of  variation." 
But  since  the  process  in  question  is  not  localised,  but  is,  as  a 
rule,  transmitted  with  measurable  velocity  from  the  seat  of 
excitation,  over  the  entire  fibre,  a  longer  or  shorter  section  of 
the  muscle  will  always  be  found  to  be  simultaneously  (at  different 
points)  in  different  phases  of  negativity.  If  the  values  of  these 
are  erected  as  ordinates  upon  the  muscle  as  abscissa,  the  resulting 
curve  resembles  in  its  form  the  curve  of  variation,  and  is  called 
the  "  excitatory  wave."  Since  the  velocity  with  which  the 
process  of  negativity  (excitation)  is  transmitted  in  the  muscle 
is  known,  as  on  the  other  hand  the  time  at  which  the  excitatory 
wave  is  propagated  its  entire  length — this  being  identical  with 
the  duration  of  the  negative  variation  at  any  definite  point  of  the 
fibre, — the  length  of  the  excitatory  wave  may  easily  be  calculated 
from  the  formula  s  =  ct  =  D  (duration  of  negative  variation)  x  V 
(velocity).  Since  the  two  values  by  which  the  length  of  the 
excitatory  wave  are  determined  differ  in  different  muscles,  and 
even  in  the  same   muscle  at  different  times,  the  length   of  the 


376  ELECTRO-PHYSIOLOGY  chap. 

excitatory  wave  naturally  varies  considerably.  Bernstein  observed 
this,  and  Kiihne,  to  whose  experiments  we  shall  return  later, 
found  that  the  velocity,  and  with  it  the  length  of  the  excitatory 
wave,  varied  considerably.  In  the  most  unfavourable  cases  the 
former  was  25  cms.  per  sec,  in  other  cases,  on  the  contrary, 
more  than  2  m.  This  recalls  the  striking  fact  that  the  same 
muscle  may  propagate  slow  and  rapid  waves  of  contraction,  and 
we  are  in  fact  in  both  cases  concerned  with  the  same  phenomenon, 
since  there  is  nothing  to  hinder  the  identification  of  "  excitatory 
wave "  and  "  wave  of  excitation."  It  only  remains,  therefore, 
to  establish  the  relations  between  this  latter  and  the  "  wave  of 
contraction."  The  fact  that  muscular  contraction  implies  a  latent 
period,  which,  according  to  Bernstein,  is  absent  in  the  "  excitatory 
wave,"  is  a  iniori  evidence  that  the  "  excitatory 
wave  outruns  the  wave  of  contraction,  partially 
at  least,  in  an  excited  muscle  fibre." 

As  early  as  1854,  indeed,  Helmholtz  stated 
that  the  negative  variation,  at  any  rate  in  its 
steepest  part  where  the  secondary  twitch  is 
excited,  was  the  precursor  of  contraction.  He 
located  it  at  the  middle,  v.  Bezold  later  on 
at  the  beginning,  of  the  latent  period.  Helm- 
holtz (22)  arranged  his  experiment  as  fol- 
FiG.  n9.-Period  of  iiega-  lows  : — The  uervc  A  of  a,  muscle  (Fig.  119) 
tive  variation.  Helm-  connected     witli     the     Writing  -  point     of     a 

holtz  s  experiment.  _  ^      ■'■_ 

myograph,  bridged  over  the  longitudinal  and 
transverse  sections  of  the  muscle  B,  the  nerve  of  which  was 
excited  by  a  break  induction  shock,  so  that  the  negative  variation 
of  the  muscle  current  of  B  produced  secondary  contraction  in 
the  muscle  A.  The  measurable  interval  between  the  moment 
of  exciting  the  primary  preparation  and  the  beginning  of  the 
secondary  twitch  of  A  was  the  sum  of  the  four  following  time- 
values  : — (i)  interval  between  arrival  of  nerve  excitation  in  A 
and  beginning  of  contraction,  i.e.  latency  period  of  A ;  (ii) 
interval  corresponding  with  propagation  of  excitation  in  nerve 
of  muscle  A,  from  point  of  excitation  to  muscle ;  (iii)  interval 
between  arrival  of  excitation  in  B,  and  moment  at  which  the 
negative  variation  excites  nerve  A  ;  (iv)  period  of  conductivity 
in  nerve  of  B.  By  deducting  the  known  intervals  (found  by 
other   experiments),    1,   2,  and    4    from   the   sum    the   required 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  377 

magnitude  3  may  be  calculated,  and  is  actually  ^Iju  ^^c. ;  i.e. 
about  ^^y  sec.  elapses  between  the  moment  of  exciting  the 
muscle  and  the  moment  of  its  most  pronounced  electrical 
variation.  Starting  with  the  length  of  the  latent  period,  as 
originally  assumed,  at  j^  sec,  the  maximum  of  the  negative 
variation  coincides  with  the  middle  of  the  period  of  latent 
excitation.  According  to  v.  Bezold  (23)  the  electrical  variation 
begins,  under  its  most  favourable  conditions,  immediately  after 
the  moment  of  excitation,  and  therefore  falls  at  the  beginning 
of  the  latent  period.  The  estimation  of  the  latter  has  been 
constantly  reduced  since  the  time  of  Helmholtz,  and  Burdon- 
Sanderson  has  recently  placed  it  much  lower  than  Tigerstedt, 
who  reckoned  it  at  0'005  sec.  for  frog's  muscle.  According  to 
Burdon-Sanderson  (24)  the  interval  between  excitation  and  the 
first  sign  of  change  of  form  is  only  0*0025  =  4^  sec,  and  since 
he  allows  an  equally  large  latent  period  to  the  negative  variation, 
there  would  thus  be  no  perceptible  interval  between  the  two 
manifestations;  whereas,  according  to  Bernstein  {I.e.  p.  192),  on 
the  other  hand,  "  each  element  of  the  muscle  fibre  completes  its 
process  of  negative  variation  before  it  enters  into  the  state  of 
contraction."  Since,  however,  on  the  one  hand,  the  preoccurrence 
of  the  electrical  variation  can  be  directly  observed  in  slowly 
contracting  muscle,  e.g.  heart  (infra),  and,  on  the  other,  it 
appears  on  theoretical  grounds  to  the  last  degree  improb- 
able that  the  excitation  itself  (i.e.  changes  in  the  contractile 
substance  associated  with  negativity)  should  possess  a  latent 
period,  the  idea  is  confirmed  that  the  beginning  of  the  wave  of 
excitation  precedes  the  contraction  wave,  by  however  small  an 
interval  (cf.  Engelmann,  25).  This  does  not,  of  course,  imply 
that  it  declines  earlier  in  Bernstein's  sense,  or  dies  away  at  any 
particular  point  before  contraction  begins  there,  for  while  it  is 
quite  conceivable  that  a  point  of  the  muscle  may  be  excited,  and 
become  negative  to  adjacent  resting  points  without  being  per- 
ceptibly contracted,  the  contrary  is  impossible,  and  every  con- 
tracted part  must  necessarily  be  assumed  to  be  in  a  state  of 
excitation  also.  In  this  sense,  therefore,  it  may  be  said  that  the 
eleetrical  loave  itself  is  an  exjjrcssion  of  contraction  (cf.  Lee,  26). 
If,  with  Bernstein,  we  assume  O'OIS  — 0'023  sees,  to  be  the 
latent  period  (which  is  not,  in  any  case,  conclusive),  and  start 
with    the   values    calculated   from  this  for  length,  duration,  and 


378  ELECTRO-PHYSIOLOGY  chap. 

velocity  of  the  excitatory  wave,  then  on  exciting  a  muscle  at 
any  gjven  point  the  excitatory  wave  would  already,  after  the 
period  of  latent  excitation,  have  traversed  a  tract  of  45—92 
mm.  in  the  fibres,  before  contraction  began  at  the  seat  of  excita- 
tion. Moreover,  the  vast  difference  that  exists,  according  to 
Bernstein,  in  the  length  of  the  two  waves,  would  also  come  into 
consideration.  While  the  excitatory  wave  is  about  10  mm. 
long,  the  wave  of  contraction  ranges  between  198  and  380 
mm.  This  last  statement,  however,  needs  consideration  when 
it  is  recognised  that  each  contracted  fibre  point  must  be 
regarded  as  "  excited,"  and  on  the  other  hand  admitted  that 
negativity  is  the  galvanic  expression  of  excitation.  The  first 
assumption  is  essentially  restricted  by  the  fact  that  in  all  recent 
experiments  the  latent  period  is  found  to  be  much  shorter  than 
was  formerly  supposed.  Moreover,  F.  S.  Lee  {I.e.)  has  recently, 
by  means  of  the  capillary  electrometer,  found  considerably  higher 
values  for  the  duration  of  the  wave  of  excitation  than  any 
previous  observer,  so  that  no  doubt  remains  that,  at  least  in 
fresh  muscle,  "  electrical  differences  of  potential,  which  are 
associated  with  contraction,  are  demonstrable  for  a  much  longer 
period  than  had  previously  been  concluded."  This  also  agrees 
with  the  idea  that  the  electrical  wave  falls  in  the  latent  period 
of  the  contraction,  and  (as  a  whole)  outlasts  it  (F.  S.  Lee).  The 
values  found  by  Lee  for  the  duration  of  the  wave  of  excitation 
are  in  fact  of  the  same  order  as  the  duration  of  the  contraction 
(0-05-0-26  sees.) 

It  thus  appears  as  though  du  Bois-Eeymond's  interpreta- 
tion of  the  secondary  contraction  was  after  all  the  only 
adequate  and  possible  conclusion — since  it  was  shown  that 
with  each  single  excitation  the  demarcation  current  of  a  muscle 
underwent  a  very  rapid  negative  variation,  which  could  be 
excited  by  a  nerve  bridging  over  the  longitudinal  and  transverse 
section,  provided  the  preparation  were  sufficiently  excitable. 
This  explanation  necessarily  underwent  considerable  modifica- 
tion when  the  justice  of  Matteucci's  original  contention  was 
established,  viz.  that  the  appearance  of  the  secondary  contraction 
is  independent  of  the  position  of  the  nerve  on  the  primary 
muscle,  since  "  parelectronomic  "  gastrocnemii,  when  excited  from 
the  nerve,  were  also  able  to  excite  a  secondary  preparation,  the 
nerve  of  which  bridged  the  longitudinal  and  natural  transverse 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  379 

sections  of  the  primary  muscle,  or  was  merely  in  contact  with 
the  latter.  It  is  obvious  that  we  cannot  here  speak  a  'priori 
of  a  negative  variation,  since  the  current  which  should  vary  is 
absent,  at  least  as  regards  any  branch  that  can  be  led  off  to  the 
galvanometer.  It  is  therefore  imperative  to  investigate  the 
galvanic  effects  of  excitation  in  the  uninjured,  currentless 
muscle.  But  before  we  enter  upon  the  complicated  relations 
of  indirect  excitation  of  the  gastrocnemius  it  is  advisable  to 
examine  the  simplest  case  of  direct  excitation  of  the  currentless 
sartorius. 

If  one  end  of  the  muscle  is  tetanised  while  leading  off  at 
the  other  end  from  the  natural  cross-section  and  a  point  on  the 
longitudinal  surface  at  about  the  middle  of  the  muscle,  a  current 
appears,  as  du  Bois-Eeymond  found,  during  excitation,  in  the 
direction  of  a  negative  variation,  even  where  no  trace  of  a 
regular  muscle  current  had  previously  been  present,  inasmuch 
as  the  tendon  end  is  positive  towards  every  point  of  the  longi- 
tudinal surface.  We  must  adopt  Hermann's  designation  of  this 
as  the  "  action  current "  because,  independent  of  the  presence 
or  absence  of  a  current  of  rest,  it  characterises  the  active  state 
of  the  muscle.  As  a  corollary  to  Hermann's  view,  the  negative 
variation  of  the  demarcation  current  was  explained  above  as 
signifying  that  the  contractile  substance  under  the  electrode 
in  contact  with  the  longitudinal  surface  becomes  more  or  less 
negative  at  the  instant  when  a  wave  of  excitation,  or  "  ex- 
citatory wave,"  passes  under  it,  when  the  original  difference  of 
potential  between  longitudinal  and  artificial  transverse  section  is 
of  course  diminished  in  proportion.  But  it  is  evident  that  the 
same  canon  of  interpretation  cannot  be  prima  facie  applied  to 
the  present  case  of  uninjured,  and  therefore  currentless,  muscle. 
For  if  we  are  to  assume  that  the  normal  ends  of  fibres,  like  all 
other  parts  of  the  muscle,  take  part  in  the  excitation  (and  there 
is  no  evidence  to  the  contrary),  they  must,  when  the  excitatory 
wave  reaches  them,  become  as  negative  as  every  preceding 
segment.  Then,  however,  under  the  given  conditions,  a 
descending  current  directed  in  the  muscle  from  longitudinal 
section  to  tendon  could  not  appear  during  tetanisation,  much 
rather  would  the  absence  of  current,  obtaining  before  the 
excitation,  continue  also  during  stimulation.  Later  on,  Her- 
mann's theory  will   be  found   to  give   a  simple  solution  of  this 


380 


ELECTRO-PHYSIOLOGY 


apparent  contradiction,  while  dii  Bois-Eeymond  (whose  inter- 
pretation of  the  negative  variation  in  the  muscle  current  will 
be  discussed  below)  finds  himself  reduced  to  the  highly 
improbable  assumption  that  the  natural,  uninjured  ends  of 
fibres,  or  parelectronomic  layer  of  the  same,  take  little  or  no 
part  in  the  excitatory  process. 

Against  this,  it  must  be  remarked  in  the  first  place  that  a 
tetanic  action  current  in  the  same  direction  may  always  be 
observed  when  the  ends  of  fibres  are  not  included  in  the 
leading-off  tract,  any  two  points  in  the  longitudinal  surface  of 
the   muscle    beimj    taken    as     the    contacts    of    the    leading-off 


N 


M 


Fig.  120. — Schema  of  the  diphasic  action  current.    (Bernstein.) 


circuit  (Hermann,  27).  The  cause  of  this  may  be  determined 
by  an  experiment  first  carried  out  by  Bernstein  (/.c.  p.  160  ff) 
with  the  aid  of  the  rheotome ;  it  is  also  valuable  in  other 
connections. 

Let  {M,  M)  be  a  regular  muscle  with  parallel  fibres,  at  one 
end  of  which  single  stimuli  are  led  in  at  equal  intervals  by  the 
rheotome  (Fig,  120),  while  between  every  two  excitations  there 
is  a  very  brief  closure  of  the  galvanometer  circuit  at  any  con- 
venient moment  of  the  pause  between  the  excitations ;  then — if 
excitation  and  galvanometer  closure  occur  simultaneously — no 
result  can  follow,  since  the  wave  of  excitation,  starting  from 
(P),  requires  a  certain  time  to  reach  the  nearest  leading -oft' 
point  {a).      But  if  the  galvanometer  circuit  is  always  closed  at 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  381 

the  moment  at  which  the  beginning  of  the  excitatory  wave  has 
reached  the  point  named,  i.e.  so  long  after  each  individual 
stimulus  as  the  wave  requires  in  order  to  travel  over  the 
distance  (P,  ct),  a  perceptible  deflection  of  the  magnet  may  be 
expected  in  the  sense  that  (a)  will  be  negative  to  the  second 
led -off  point  (h),  if  it  is  correct  that  each  point  under  the 
excitatory  wave  is  negative  to  each  point  beyond  it.  If  the 
closure  of  the  galvanometer  circuit  is  advanced  still  further  in 
the  same  direction,  so  that  other  superficial  points  of  the  curve 
of  variation  are  excluded,  the  effects  must  at  first  increase  in 
the  same  direction,  reach  a  maximum  when  the  excitatory 
wave  is  at  its  acme,  and  finally  decline  to  zero  when  the 
entire  wave  of  excitation  has  passed  the  point  (a).  Starting 
from  Bernstein's  computation  of  10  mm.  for  the  length  of  the 
wave,  with  the  two  leading-off  electrodes  at  more  than  10  mm. 
from  each  other,  the  end  of  the  excitatory  wave  will  have 
passed  the  point  (ct)  before  the  first  part  reaches  (h),  and  the 
same  still  obtains  a  little  later,  provided  the  electrodes  are 
sufficiently  far  apart.  At  a  certain  adjustment  of  the  rheotome 
slider,  corresponding  with  this  interval,  there  will  therefore  be 
hardly  any  difference  in  potential  between  (ct)  and  (h).  It  is  not 
till  the  closure  of  the  galvanometer  circuit  is  so  delayed  after  each 
single  stimulus  that  the  first  part  of  the  excitatory  wave  has 
already  reached  the  point  (5)  that  there  Avill  again  be  any 
marked  deflection,  and  that  in  a  direction  diametrically  oiyposite 
to  the  earlier  variation,  since  {h)  is  now  negative  to  («).  The 
difference  in  potential  increases  as  before  with  further  advance- 
ment of  the  galvanometer  closure,  attains  a  maximum,  and 
finally,  when  the  end  of  the  excitatory  wave  has  passed  under 
(h),  declines  to  zero.  Thus,  on  leading-off  from  two  symmetrical 
longitudinal  points  of  a  muscle,  rhythmically  excited  (tetanised) 
by  induction  shocks,  there  is,  after  each  single  stimulus,  a  double 
variation,  or,  more  properly,  a  diiJhasic  current  of  action.  Bern- 
stein, to  wdiom  we  owe  the  discovery  of  this  fact,  named  the 
current  which  appears  while  the  wave  of  excitation  is  passing 
under  the  point  a,  and  has  the  direction  of  the  lower  arrow 
in  the  muscle  (Fig.  120),  the  negative  variation,  that  which 
follows  it  in  the  direction  of  the  upper  arrow,  the  2^ositive 
variation.  It  is  evident  that  the  absolute  mao-nitude  of 
the   deflection  produced  by    the  first  action  current  should  be 


382  ELECTRO-PHYSIOLOGY 


exactly  parallel  with  that  derived  from  the  second ;  but 
according  to  Bernstein  this  never  is  the  case,  the  positive  being 
always  smaller  than  the  negative  variation.  Accordingly,  the 
excitatory  wave  decreases  in  amplitude  as  it  is  propagated 
along  the  muscle  -  fibres ;  in  other  words  (at  least  in  excised 
muscle),  it  is  decremental.  The  double  action  current  observed 
after  each  single  excitation  in  uninjured,  currentless  muscle 
may  be  termed,  after  Hermann  (27),  the  "phasic  current  of 
action."  The  first  phase  is  directed  from,  the  second  towards 
the  seat  of  excitation.  If  one  of  the  leading- off'  contacts  is 
applied  to  an  artificial  cross-section,  the  corresponding  phase  will 
make  its  appearance.  Since  the  galvanometer  magnet  is  much 
too  insensitive  to  respond  by  corresponding  deflections  to  these 
opposite  currents  (which  follow  with  extraordinary  rapidity  in 
tetanising  excitation),  we  should  anticipate  that  on  leading  off" 
without  current  from  two  points  of  the  longitudinal  section, 
there  would  be  no  effect  even  during  tetanus.  That  this  is 
actually  not  the  case  may  be  explained  from  the  fact  that  the 
excitatory  wave  decreases  in  amplitude  during  its  transmission 
through  the  muscle ;  it  follows  directly  that  on  leading  off 
from  two  longitudinal  points  of  an  uninjured,  currentless, 
parallel -fibred  muscle,  a  difference  in  electrical  potential  must 
appear  between  the  two  points,  when  one  end  is  tetanised  by 
an  ordinary  induction  coil :  the  longitudinal  contact  proximal 
to  the  seat  of  excitation  must  always  be  negative  to  the  distal 
point,  since  the  latter,  owing  to  the  decrement  of  the  excitatory 
wave,  must  always  be  less  negative  than  {i.e.  relatively 
positive  to)  the  former.  Such  an  action  current  is  in  fact 
present  in  tetanus,  and  has  been  confirmed  by  clu  Bois-Eeymond 
and  Hermann.  The  latter  found  the  E.M.F.  of  this  current, 
which  he  described,  from  reasons  given  above,  as  the  "  decre- 
mental action  current  of  tetanus,"  to  be  of  considerable  pro- 
portions (0  "00  2  —  0 '02  Dan.)  Du  Bois-Eeymond  originally 
believed  that  decremental  action  currents  were  only  to  be 
observed  on  fatigued,  moribund  muscle,  i.e.  that  the  excitatory 
wave  only  diminished  in  these  cases.  Hermann,  however, 
showed  that  the  decrement  obtains  immediately  after  making 
the  preparation.  Since  the  excitatory  wave  becomes  smaller 
in  proportion  as  it  is  farther  from  the  seat  of  excitation,  the 
individual  transverse  sections  of  a  muscle  tetanised  at  one   end 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  383 

must  be  the  less  negative,  the  nearer  they  lie  to  the  end  not 
excited.  Hermann  gave  direct  proof  of  this  by  leading  off 
from  a  number  of  loops  of  thread,  placed  round  a  regular 
muscle  with  parallel  fibres ;  one  end  of  the  muscle  was  tetanised, 
and  the  E.M.F.  of  the  action  current  determined  between  each 
pair  of  contacts.  He  found  it  "  approximately  proportional  to 
the  relative  distance  of  the  loops  and  quite  independent  of  their 
position."  "  Each  point  traversed  by  the  excitation  is  thus, 
during  tetanus,  the  seat  of  electromotive  force,  homodromous 
with  the  wave  of  excitation."  And  thus  it  appears  that  the 
"  negative  variation "  in  its  original  manifestation  is  no  more 
than  a  special  case  of  the  action  current  in  tetanus,  in  which 
the  reciprocal  phases  ensue  on  leading  off  from  an  artificial 
transverse  section. 

Since  under  normal  conditions  the  muscle  is  always  excited 
indirectly,  i.e.  from  the  nerve,  a  special  interest  attaches  to  the 
investigation  of  the  action  current  in  uninjured  muscle  with  this 
kind  of  excitation ;  the  more  so  as  all  the  earlier  experiments  on 
the  negative  variation  were  made,  from  motives  of  convenience, 
with  what  is  intrinsically  the  least  suitable  object — the  frog's 
gastrocnemius  tetanised  through  its  nerve.  The  same  uninjured 
muscle  was  also  the  subject  of  the  first  series  of  exact  analytical 
experiments  made  on  the  action  current,  with  indirect  excitation, 
and  led  off  from  the  two  tendinous  ends  by  Sigmund  Mayer  (28) 
under  Bernstein's  direction,  and  with  his  rheotome.  The  compli- 
cated manifestations  observed  (accounted  for  by  every  possible 
interpretation  and  explanation)  first  became  intelligible  when 
Hermann,  in  1877,  began  to  investigate  the  action  current  of  regu- 
larly constructed  parallel-fibred  muscles,  with  indirect  excitation. 
With  our  present  knowledge  of  the  relations  between  nerve  and 
muscle  it  is  legitimate  to  assume  that  the  excitation  is  discharged 
at  a  definite  point  in  every  muscle-fibre,  on  stimulating  the  nerve 
fibre  belonging  to  it,  i.e.  at  the  nerve  end-plate,  which  is  situated 
between  the  contractile  substance  of  which  it  is  the  continuation, 
and  the  nerve-fibre  of  which  it  is  the  conducting  organ.  We  shall 
presently  have  to  examine  the  histological  and  physiological  relations 
between  nerve  and  muscle  in  detail ;  for  the  moment  it  is  enough 
to  say  that  it  has  been  ascertained  that  the  nerve-fibre  is  connected 
with  only  a  limited  tract  of  the  muscle-fibre  or  fibres  belonging 
ing  to  it,  which  by  no  means  prevents  the  same  muscle- fibre  from 


384  ELECTRO-PHYSIOLOGY  chap. 

being  served  at  different  i^oints  by  a  plurality  of  nerve-fibres.  The 
theory  that  has  recently  found  much  support,  from  J.  Gerlach  in 
particular,  to  the  effect  that  there  is  no  proper  nerve-ending  in 
muscle,  since  the  nerve  as  it  enters  passes  over  the  contractile 
substance  in  the  whole  extension  of  the  muscle,  ramifying  every- 
where between  the  elements  of  the  muscle-fibre,  in  the  form 
of  the  finest  varicose  fibrils,  must  now  be  regarded  as  refuted, 
the  more  so  since  it  has  been  shown  that  Gerlach's  nerve-fibrils 
are  really  no  more  than  the  darkly-stained  (gold  chloride),  and 
therefore  strongly -reducing,  interfibrillar  substance  (sarcoplasm) 
of  the  muscle.  If  the  excitation  thus  starts,  with  indirect  stimu- 
lation, from  the  points  of  the  fibre  corresponding  with  the 
nerve-ending,  it  must  necessarily  be  transplanted  thence  in  an  un- 
dulatory  form  on  either  side  through  the  fibre.  This  is  no  mere 
theoretical  conclusion,  but  receives  direct  confirmation  both  from 
histological  investigation  and  from  physiological  experiment.  As 
regards  the  former,  weighty  evidence  has  recently  been  contributed 
by  Fottinger,  Eollett,  and  others  to  the  effect  that  the  "  fixed 
wave  of  contraction  " — which  is  easily  demonstrated  in  the  muscle- 
fibres  of  many  insects,  after  proper  treatment  of  the  living  tissue 
with  hardening  and  preserving  fluids — obtains  mainly  at  the  point 
where  the  nerve  enters,  so  much  so  indeed  that  the  maximum  of 
contraction,  i.e.  the  crest  of  the  wave,  usually  falls  in  the  centre 
(sole)  of  Doyer's  expansion.  This,  in  addition  to  direct  observation 
of  still  living  fibres,  shows  unequivocally  that  the  entrance  of 
the  nerve  is  the  starting-point  of  an  undulatory  contraction  pro- 
pagated on  either  side  through  the  muscle. 

The  advance  of  the  negative  wave  of  excitation  is  demonstrated 
with  equal  precision  in  the  galvanometer,  on  indirect  excitation 
of  the  entire  muscle,  thus  obviating  the  doubt  expressed  by  du 
Bois-Eeymond  as  to  the  undulatory  nature  of  excitation,  when  the 
muscle  is  stimulated  from  its.  nerve.  The  adductor  magnus  of  the 
frog  is  in  all  respects  a  suitable  preparation,  the  nerve  entering 
by  the  centre  of  the  muscle ;  this  muscle  is  a  little  more  trouble- 
some to  prepare  than  the  usual  gastrocnemius  and  sciatic  nerve- 
muscle  preparation,  but  the  regularity  and  certainty  of  its  results 
are  ample  compensation.  We  may  assume  from  the  previous 
experiments  that  such  a  preparation,  on  the  excitation  of  its 
nerve  by  induction  shocks,  will  respond  exactly  like  the  muscle 
excited  directly  at  the  nerve  end-plate,  in  special  cases,  i.e.,  at  the 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  385 

centre.  Hence  it  is  a  great  advantage  to  lead  off',  in  indirect 
excitation,  from  the  actual  seat  of  the  excitatory  process.  If  each 
nerve-ending  lay  exactly  in  the  middle  of  the  corresponding  fibre 
of  the  parallel-fibred  muscle,  a  negative  wave  of  excitation,  or  con- 
traction, would  obviously  be  propagated  from  it  in  both  directions 
through  the  muscle  at  the  moment  of  excitation.  Then,  on  lead- 
ing off"  from  the  middle  and  tendon  end  of  such  a  muscle  to  the  gal- 
vanometer, while  single  shocks  were  sent  into  the  nerve  at  equal 
intervals  by  a  Bernstein  rheotome,  a  diphasic  action  current  would 
be  demonstrable,  consisting  of  a  first  "  atterminal  (abnerval),"  and 
a  second  "  abterminal  (adnerval)  "  phase.  Such  a  response  was 
actually  found  by  Hermann  in  his  experiments  wdth  the  sartorius 
preparation.  Both  halves  of  the  muscle  at  first  indicated  an 
atterminal  current  directed  from  the  centre  to  each  tendon  end, 
while  a  little  later,  i.e.  at  the  interval  required  by  the  excitatory 
wave  to  traverse  the  muscle  from  centre  to  tendon  end,  an  abter- 
minal action  current  appeared,  which,  owing  to  the  decrement  of 
the  exciting  wave,  was  always  weaker  than  the  first  current. 
On  leading  off  from  both  tendon  ends,  we  have  at  each  moment 
the  algebraic  sum  of  the  effects  in  either  half;  this  sum  of 
course  =  0  in  a  properly  symmetrical  muscle,  in  others  its  sign 
varies  with  the  time -interval.  These  experiments  of  Hermann 
give  physiological  proof  of  the  undulatory  course  of  excitation  in 
indirect  stimulation,  and  we.  may  now  proceed  to  consider  the 
action  current  in  its  more  complicated  examples,  with  indirect 
excitation  of  the  gastrocnemius.  S.  Mayer  (I.e.)  found  first  a 
descending  and  then  an  ascending  action  current,  on  leading 
off  from  both  tendinous  ends  of  this  muscle,  after  each  single 
excitation  ;  or,  as  it  was  then  expressed — because  the  first  current 
was  identified  with  the  negative  variation  of  the  muscle  corroded 
at  the  achilles.  expansion — a  variation  first  negative  and  then  posi- 
.  tive  appeared,  a  fact  confirmed  later  by  du  Bois-Eeymond  with 
Bernstein's  rheotome,  which  S.  Mayer  had  also  employed,  and  by 
Hermann  with  the  (non-repeating)  "fall-rheotome"  described  above. 
If  the  tendo  achilles  was  corroded,  the  ascending  (positive)  half  of 
the  current  was  absent.  Holmgren  (29),  moreover,  by  means 
of  a  light  magnet  (without  rheotome),  had  frequently  observed, 
before  Mayer,  a  diphasic  variation  on  the  gastrocnemius,  as  well 
as  cases  of  simple  positive,  and  negative  variations.  According  to 
Hermann  the  gastrocnemius  may  be  regarded,  diagrammatically,  as 

2  c 


386 


ELECTRO-PHYSIOLOGY 


a  muscle  rhombus,  and  it  is  tolerably  accurate  to  say  that  the 
nerve-ending  lies  in  the  middle  of  each  fibre  (Fig.  121).  But 
then  it  follows  that  all  the  points  corresponding  with  the  upper 
contacts  {a,  h),  i.e.  the  thick  part  of  the  muscle,  must  be  affected 
more,  and  earlier,  by  the  waves  of  excitation  from  the  nerve-endings 
{a,  yS)  than  the  lower  ends  of  fibres,  corresponding  with  the  tendo 
achilles.  Thus  there  will  at  first  be  a  descending,  and  subse- 
quently a  weaker  ascending,  current  of  action.  "  The  upper  half 
of  the  muscle,  on  the  contrary,  should  vary  first  in  an  ascending 
and  then  in  a  descending  direction ;  here,  however,  the  structure 
of  the  muscle  is  essentially  different ;  the  main  part  of  the 
current   ('  Neigungstrom ')  is  prevented  by  the  folds  of  the  upper 

expansion  from  producing  any  ex- 
ternal effect,  so  that  in  the  first  place 
the  abterminal  phase  of  the  upper 
half  of  the  muscle  is  hardly  per- 
ceptible, and  in  the  second  the  upper 
tendon  as  a  whole  must  be  regarded 
as  a  lead-off  from  the  longitudinal 
section.  On  leading  off  from  both 
tendons,  the  effects  are  consequently 
not  very  dissimilar  to  those  with 
the  lead-off  from  belly  and  achilles 
tendon.  There  is  thus  no  doubt 
that  the  first  descending  phase 
starts,  not  from  the  expansion  of 
the  tendo  achilles,  but  from  the 
longitudinal  section,  while  the  second  ascending  phase  does 
originate  at  the  achilles  expansion "  (Hermann).  With  the 
corrosion  of  the  latter,  the  second  phase  naturally  dies  out,  since 
the  ends  of  fibres  then  become  negative  without  it.  And  this  of 
course  applies  to  tetanus,  in  which  du  Bois-Eeymond  first  observed 
the  descending  effect  in  the  currentless  gastrocnemius,  since, 
generally  speaking,  only  the  algebraic  sum  of  the  opposed  action 
currents  can  be  detected.  But,  owing  to  the  preponderance  of 
the  first  descending  phase,  the  effect  is  actually  descending.  It 
is  unnecessary  here  to  enter  into  further  minutise  of  electro- 
motive action  in  the  excited  gastrocnemius,  since  no  new 
theoretical  data  can  be  expected  from  it.  We  need  only 
mention  that  Matthias  (30)  has  recently  (by  Hermann's  "  rheo- 


FiG.  121. 


IV  ELECTROMOTIVE  ACTIOX  IX  MUSCLE  387 

tachygraphic "  method,  as  described  above)  published  a  graphic 
record  of  the  gastrocnemius  action  current,  which,  on  leading  off 
from  the  tendo  achilles  and  from  a  point  proximal  to  the  nervous 
equator,  gives  double-topped  curves,  in  which  the  first  descending 
phase  is  succeeded  by  a  second,  weaker,  ascending  variation,  after 
which  the  magnet  returns  to  its  zero  with  some  insignificant 
deflections  (Fig.  122). 

This  dissimilarity  is  apparently  due  to  a  partial  superposition 
of  the  two  phases ;  the  excitation  has  not  entirely  passed  the 
upper  lead-off  before  it  reaches  the  lower.  The  gastrocnemius 
curve  of  electrical  variation  is  even  more  complicated  on  lead- 
ing off  from  the  centre  and  tendo  achilles,  as  in  the  observa- 
tions of  Lee  which  we  have  frec[uently  referred  to,  in  which  the 
more  sluggish  galvanometer  is  replaced  by  the  sensitive  capillary 
electrometer.  The  rheotome  method  can  also  be  applied  here. 
The  curve  (Fig.  123,  a)  corre- 
sponds with  a  triphasic  varia- 
tion, its  two  negative  sections 
being  separated  by  a  double- 
topped,  positive,  and  very  steep 
segment.  The  duration  of  the 
entire  process  amounts  to  0'26 
sec,  a  value  which  we  have 
seen  to  be  approximately  equi-  ^^^  ^^^ 

valent   to    the    duration   of    a 

twitch  in  the  muscle.  The  wave  of  variation  in  the  sartorius,  on 
the  other  hand  (when  led  off'  from  the  middle  and  end  of  the  muscle), 
was  found  by  Lee  to  be  diphasic,  no  conspicuous  decrement  being 
visible  in  the  fresh,  uninjured  muscle.  Both  sections  exhibited  a 
tolerably  symmetrical  figure  (Fig.  123,  l).  If,  however,  the  tendon 
end  of  the  muscle  is  injured  ever  so  slightly,  the  first  ("  negative  ") 
phase  prevails,  and  the  second  may  disappear  entirely,  as  shown 
by  the  lower  curve  of  the  same  figure.  In  this  case  the  variation, 
which  is  now  monophasic,  does  not  appear  perceptibly  shorter 
than  the  sum  of  the  two  earlier  phases,  which  again  implies 
superposition  of  the  two  components.  The  triphasic  wave  of  the 
gastrocnemius  again  (in  progressive  fatigue,  or  injury,  of  the  lower 
end  of  the  muscle)  undergoes  alteration  in  the  sense  that  the  middle 
positive  section  disappears,  or  is  merely  indicated.  For  the  rest, 
the  fatisue  chansjes  in  the  curve  of  electrical  variation  in  striated 


388 


ELECTRO-PHYSIOLOGY 


muscle  have  a  special  interest,  inasmuch  as  they  once  more 
illustrate  the  intimate  relations  {sui^ra)  which  exist  between  the 
current  of  action  and  the  phenomena  of  contraction.  According 
to  Lee,  the  curve  of  the  former  alters  in  the  same  sense  as  that  of 
the  twitch,  since  on  the  one  hand  it  decreases  in  height  by  the 
reduction  of  all  its  ordinates,  while  on  the  other  its  time-relations 
are  more  extended. 

We    have    seen     that    all    electromotive    manifestations    in 


Fig.  123. — a,  Triphasic  curve  of  variation  in  gastrocnemius  muscle  ;  6,  diphasic  curve  of  variation 
of  sartorius  muscle.     Above  is  the  normal,  below  the  injured,  muscle.    (P.  S.  Lee.) 


isolated  muscle,  with  direct  or  indirect  excitation,  may  be  easily 
explained  without  further  hypothesis  by  Hermann's  alteration 
theory,  on  the  simple  assumption  that  excited  fibres,  like  moribund 
fibres,  are  electro  -  negative  to  normal  or  resting  fibres.  The 
fundamental  data  of  this  theory  render  such  a  proposition 
self-evident,  since  in  both  cases  there  is,  in  Hering's  sense,  a 
descending    alteration    of    the    living    matter,    so     that    action 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  389 

current  and  rest  current  must  alike  be  referred  to  the  same 
cause,  "  since  both  are  to  be  regarded  as  the  external  symptom  of 
a  different  ratio  of  descending  change  in  the  two  parts  of  the 
muscle  brought  together  in  the  circuit."  Accordingly,  there  is 
as  little  essential  difference  between  action  current  and  rest 
current,  as  between  excited  and  dying  muscle-substance.  From 
this  point  of  view  it  is  meaningless  to  ask  whether  the  "  potassium 
current "  in  muscle  (as  above)  is,  or  is  not,  to  be  regarded  as  an 
action  current.  The  circumstance  that  it  appears  in  etherised 
muscle  proves  as  little  against  the  former  assumption  as  the 
presence  of  the  normal  demarcation  current,  under  the  same  con- 
ditions, against  the  latter. 

From  the  standpoint  of  the  molecular  theory,  the  electro- 
motive response  of  uninjured,  currentless  muscle  encounters  great 
difficulties  of  interpretation,  which  can  only  be  met  by  supple- 
mentary hypothesis.  It  is  superfluous  to  enter  on  the  detailed 
discussion  of  these,  since  they  are  based  on  the  parelectronomic 
theory,  the  invalidity  of  which  can  hardly  be  disputed.  A  brief 
exposition  of  the  fundamental  canon  by  which  du  Bois-Eeymond 
interpreted  the  negative  variation  of  the  demarcation  current 
is  all  that  is  required.  He  derives  it  essentially  from  a  diminu- 
tion of  E.M.F.  in  the  "  molecules,"  or  from  their  rearrangement 
in  a  form  less  centrifugally  active.  Bernstein's  new  "  electro- 
chemical theory  "  also  postulates  a  "  decrement  of  charge  in  the 
molecules,"  from  which  he  explains  the  negativity  of  each  point 
excited.  "  If  the  excitatory  wave  is  propagated  to  the  cross-section, 
the  charges  of  the  molecules  also  decrease  pari  passu.  When  the 
wave  reaches  the  cross-section  it  fails  to  produce  any  current  in 
the  opposite  direction,  i.e.  second  positive  phase  of  variation, 
because  the  charges  of  the  molecules  are  always  the  same  on 
the  side  towards  the  cross-section."  In  order  to  explain  the 
electromotive  action  of  currentless  muscle,  du  Bois-Eeymond  is 
forced  into  the  hypothesis  that  the  parelectronomic  layer,  or  tract, 
at  the  natural  cross-section  takes  little  or  no  part  in  the  negative 
variation,  while,  according  to  Bernstein,  the  uninjured  ends  of 
fibres  react  like  any  other  longitudinal  points.  Du  Bois-Eeymond 
believed  that  the  breaking  of  the  excitatory  wave  upon  the 
natural  cross-section  was  the  direct  cause  of  parelectronomy, 
since  he  held  that  this  was  favourable  to  the  development  of  the 
parelectronomic  molecules. 


390  ELECTRO-PHYSIOLOGY  chap. 

From  all  this  we  may  surely  conclude  in  favour  of  the  greater 
simplicity  of  Hermann's  alteration  theory,  the  more  so  since,  as  we 
shall  see  in  the  sequel,  it  brings  under  the  same  comprehensive 
point  of  view  those  electromotive  reactions  in  living  tissues  (gland 
currents  and  vegetable  currents),  which  have  hitherto  defied  the 
molecular  theory.  Finally,  it  is  elevated  above  the  rank  of  an 
arbitrary  hypothesis  adjusted  to  the  facts,  by  a  series  of  experi- 
mental researches,  which  leave  no  doubt  as  to  the  justice  of  its 
fundamental  conception. 

In  addition  to  all  the  evidence  above  quoted,  re,  "  rest  current  " 
and  action  current  in  the  muscle  (in  respect  of  which  the  alteration 
theory  is  luminous),  a  few  data  remain,  which  are  best  subjoined 
in  this  connection.  Foremost  among  these  is  the  electromotive 
reaction  of  the  so-called  idio-ynuscular  contraction.  We  know  that 
in  moribund  muscle,  especially  in  warm-blooded  animals,  conduc- 
tivity disappears  much  earlier  than  excitability.  The  contractile 
substance,  as  Funke  expresses  it,  acquires  more  and  more  the 
properties  of  a  viscous  mass,  which  tends  to  retain  the  local 
impression  instead  of  propagating  it.  Eventually,  v/ith  localised 
excitation,  a  merely  local  contraction  results  in  the  fibres,  and  is 
usually  persistent.  Hence,  as  it  were,  a  fixed  wave  of  contraction 
arises,  extending  over  a  greater  or  lesser  section  of  the  fibres. 
The  local  persistent  contraction  must,  however,  correspond  with 
localised  persistent  excitation,  and  this  again  induces  negativity 
towards  normal  points  of  fibres.  As  early  as  1857,  i.e.  ten  years 
before  the  formulation  of  the  alteration  theory,  Czermak'  gave 
proof  that  when  the  prepared  nerve  of  a  frog  falls  on  a  muscle 
with  an  idio-muscular  swelling,  so  as  to  bridge  the  latter  and  a 
normal  longitudinal  point,  a  twitch  ensues,  thus  demonstrating  a 
P.D.  between  the  swelling  on  the  one  hand  and  the  uninjured 
surface  on  the  other.  Later  investigations  of  Kiihne  and  Harless 
prove  that  the  swelling  is  invariably  negative  towards  all  other 
points  of  fibre. 

We  have  observed  repeatedly  (Biedermann,  16)  that  negative 
zones  may  be  present  also  in  the  continuity  of  the  frog's  sartorius. 
These  are  due  to  partial  persistent  contraction  of  the  otherwise 
uninjured  muscle,  and  sometimes  give  rise  to  very  powerful 
currents.  It  is  obvious  that  this  may  simulate  the  effect  of  a 
parelectronomic  layer  of  measurable  dimensions  (parelectronomic 
tract)  at  the  uninjured  ends  of  the  fibre,  since  it  is  conceivable  in 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  391 

such  a  case  that  superficial  corrosion  of  the  natural  cross-section 
proximal  to  the  tendon  might  not  immediately  develop  a  normal 
current,  if  the  negativity  of  the  leading-off  contact  of  the  longi- 
tudinal section  is  equal  to,  or  greater  than,  that  of  the  artificial 
cross-section  at  the  end  of  the  muscle.  Such  a  wave  of  contrac- 
tion is  easily  produced  at  any  given  point  of  a  muscle  with 
parallel  fibres  by  the  local  application  of  veratrin  solution,  which, 
of  course,  retards  the  decline  of  the  excitation  very  considerably. 
Hermann  obtained  the  same  .result  by  energetic  cooling  of  the 
muscle.  And  lastly,  if  it  counts  as  the  touchstone  of  a  theory 
that  new  facts  can  be  predicted  upon  its  basis,  the  "  secondary 
electromotive  manifestations  "  must  be  cited,  to  which  we  shall 
return  later. 

After  it  had  been  ascertained  from  experiments  on  isolated 
muscles  that  the  state  of  activity  is  accompanied  by  electro- 
motive alterations  demonstrable  on  the  galvanometer,  it  became  a 
desideratum  to  establish  the  same  for  uninjured  muscle  in  situ, 
in  man  and  other  warm-blooded  animals.  Du  Bois-Eeymond 
accordingly,  with  admirable  perseverance,  carried  out  a  research 
which  is  a  pattern  of  sustained  and  deliberate  investigation.  If 
his  attempts  to  discover  differences  of  potential — in  the  sense  of  a 
"  restincT  muscle  current  " — through  the  skin  of  the  intact  frog  were 
frustrated  by  the  strong  electromotivity  of  the  skin  itself,  the 
experiment  was  no  less  difficult  on  the  human  subject.  But  we 
need  not  dwell  on  the  point,  since  there  now  appears  as  little 
reason  for  ascribing  demonstrable  electromotive  activity  to  human 
muscles  during  rest,  as  to  those  of  the  frog  or  any  other  animal. 
On  the  other  hand,  du  Bois-Eeymond's  attempts  to  demonstrate 
currents  that  could  be  led  off  externally  during  voluntary  con- 
traction, or,  in  the  language  of  his  theory,  the  negative  A^ariation 
of  the  pre-existent  muscle  current,  were  crowned  with  success. 

His  classical  experiment,  which,  when  first  published,  created 
an  enormous  interest,  is  arranged  as  follows  :  One  or  more  fingers 
(preferably  the  forefingers)  of  each  hand  dip  into  the  vessels  of 
conducting  fluid,  which  again  are  conveniently  connected  with  the 
terminals  of  the  galvanometer  or  multiplier  circuit  (Fig.  124). 
When  the  magnet  has  come  to  rest  under  the  influence  of  the 
natural  (and  usually  insignificant)  current  which  results  from  in- 
equalities in  the  two  points  of  the  skin  from  which  the  current  is 
led  off,  a  sharp  contraction  of  the  muscles  of  one  arm  generally 


392 


ELECTRO-PHYSIOLOGY 


causes  an  effect  in  the  direction  of  an  ascending  current 
in  the  arm,  which,  according  to  the  later  measurements  of 
Hermann,  has  a  very  low  potential  (0'0014— 0'0023  Dan.) 
An  analogous  result  is  obtained  on  leading  off'  from  both  feet. 
In  order  that  the  experiment  may  succeed  it  is  essential  that  the 
voluntary  muscular  action  should  be  as  vigorous  as  possible.  Du 
Bois-Eeymond  strained  his  arm  until  "  the  muscles  appeared  as 
hard  as  boards,  the  arm  shook  violently,  and  after  some  seconds 
a  lively  sensation   of  warmth  was  experienced."      Sometimes,  as 


Fig.  124. — Du  Bois'  "voluntary  experiment."    (Du  Bois-Reymond.) 

proposed  by  Mousson,  a  battery  was  formed  by  the  co-operation 
of  several  persons,  a  vessel  of  concentrated  salt  solution  being 
placed  between  two,  into  which  each  person  dipped  a  finger,  and 
simultaneously  stretched  one  arm  (on  the  same  side).  All  these 
galvanic  manifestations  were  characterised  by  a  long  after-effect, 
as  well  as  by  inability  to  evoke  secondary  excitation  in  the 
physiological  rheoscope,  to  which  we  shall  return  later.  This  fact 
in  itself  is  in  no  way  prejudicial  to  du  Bois-Eeymond's  dictum  that 
the  effect  under  discussion  is  the  expression  of  the  negative 
variation  of  the  muscle  current  in  the  human  limb. 

On  the  other  hand,  various  other  considerations  have  been 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  393 

brought  forward,  which  relate  partly  to  the  direction  of  the 
current  observed,  partly  to  the  possibility  of  referring  it  to 
changes  of  temperature  in  the  muscle,  or  electromotive  action 
in  the  skin,  however  originated.  As  regards  the  first  point,  the 
contradiction  was  emphasised  between  the  descending  effect  in 
muscular  contraction  of  the  frog's  leg,  and  the  ascending  current 
in  the  arm  (or  foot)  of  the  human  subject.  Du  Bois-Eeymond 
indeed  found  that  a  P.D.  did  exist  in  the  skinless  leg  of  the 
rabbit  in  the  sense  of  a  descending  "  rest  current,"  with  a  corre- 
sponding ascending  negative  variation.  With  regard  to  Hermann's 
theory  as  applied  to  the  currents  of  groups  of  muscles,  i.e.  whole 
extremities,  neither  the  above  objection,  nor  du  Bois'  proof  of  the 
corresponding  variation  in  the  leg  of  the  rabbit,  need  detain  us. 
On  tlie  other  hand,  in  the  commission  appointed  by  the  Paris 
Academy  to  inquire  into  du  Bois-Eeymond's  experiments  on  man, 
the  elder  Bequerel  did  raise  an  objection  against  his  inter- 
pretation, which  we  must  examine  more  closely,  since  in  spite  of 
du  Bois  Eeymond's  objection  it  has  subsequently  been  tlioroughly 
substantiated. 

According  to  Bequerel,  voluntary  tetanus  of  the  arm  produces 
increased  secretion  from  the  skin  of  the  finger,  in  cousequence  of 
which  the  electromotive  properties  of  the  skin  itself  may  undergo 
alteration.  And  when  du  Bois-Eeymond  himself,  at  Bequerel's 
request,  dipped  the  forefingers  of  both  hands  into  the  leading-in 
vessels,  after  voluntarily  contracting  and  relaxing  one  arm,  there 
was  in  fact  "  a  weak  effect  in  the  same  direction  as  if  the 
arm  belonging  to  the  immersed  finger  had  been  contracted  " ;  but 
this  was  referred  to  the  prolonged  after-effect  {supra)  of  the 
supposed  negative  variation.  Du  Bois  considered  the  follow- 
ing experiment  to  be  conclusive  in  favour  of  his  interpretation. 
The  hand  and  lower  part  of  the  arm  were  confined  in  a  gutta- 
percha bag,  bound  to  the  arm  below  the  elbow^,  to  produce 
local  perspiration.  The  same  parts  were  further  bound  with  a 
woollen  cloth.  After  some  time  the  perspiring  arm  was  com- 
pared with  the  normal  limb  by  the  usual  galvanometric  method, 
on  which  it  appeared  that  the  former  was  not,  as  might  have 
been  expected  from  Bequerel's  theory,  negative,  but,  on  the 
contrary,  positive  to  the  latter.  That,  notwithstanding,  there 
was  in  du  Bois-Eeymond's  voluntary  experiment  nothing  more 
than  the  effect  of  a  secretion  current,  was  first  ascertained  at  a 


394 


ELECTRO -PHYSIOLOGY 


much  later  period  by  Hermann,  to  wliom  we  are  indebted  for 
the  first  proof  of  true  galvanic  muscular  effects  produced  in  the 
living  human  subject  by  the  current  of  action.  In  supplementing 
his  investigations  on  the  action  current  in  frog  muscles,  Hermann 
endeavoured  in  the  first  place  to  demonstrate  on  a  single  con- 
venient group  of  muscles  the  anticipated  decremental  current  of 
action  in  tetanus.  For  this  purpose  he  selected  the  forearm, 
leading  off  from  the  thick  part  of  the  flesh,  and  from  the  prox- 
imity of  the  wrist,  by  appropriate  electrodes.  These  electrodes 
consisted  of  thick  ropes,  saturated  with  ZnSO^,  looped  round  the 
parts  of  the  arm  as  above.  Yet  the  expected  (descending)  current 
failed  to  appear  here,  as  in  corresponding  experiments  on  the 
thigh ;  only  small  and  irregular  deflections  were  visible.  It 
thus  seemed  questionable  whether,  under  the  conditions  described, 
there  was  any  development  of  a  decremental  action  current  in 
human  muscle  during  voluntary  excitation.  Hermann  in  con- 
sequence applied  himself,  with 
far  greater  result,  to  the  task  of 
investigating  the  phasic  action 
current  under  the  same  condi- 
tions, but  with  artificial  excita- 
tion from  the  nerve  (27).  As 
was  stated  above,  a  diphasic 
current  may  be  demonstrated  by 
means  of  the  rheotome  method, 
between  every  two  points  of  an 
uninjured  muscle,  directly  or  in- 
directly excited,  the  first  phase  being  abnerval,  the  second  adnei- 
val,  in  direction.  In  consequence  of  the  decrement  of  the  ex- 
citatory wave  in  excised  muscle,  the  second  phase  is  distinctly 
weaker  than  the  first.  The  arrangement  of  the  experiment  is 
shown  in  Tig.  125,  after  Hermann. 

The  stimuli  must  be  so  strong  that  vigorous  twitches  ensue 
in  the  muscles  of  the  forearm.  The  results,  which  consisted  in 
the  appearance  of  a  diphasic  action  current,  at  first  descending 
(atterminal),  and  subsequently  ascending  (abterminal),  were  so 
regular  that  Hermann  was  able  to  denote  this  experiment  as  one 
of  the  most  certain  in  electro-physiology,  "  giving,  without  ex- 
ception, better  and  more  extensive  results  in  man  than  in  the 
frog."      The  same  results  were  obtained  on  leadino-  off  from  the 


Fig.  125. — Diphasic  action  current  in  the 
human  forearm.  On  the  right,  an  un- 
polarisable  rope  electrode. 


IV  ELECTROMOTIVE  ACTIOX  IX  MUSCLE  395 

upper  muscles  of  the  I'orearin  also,  as  described  in  Fig.  125,  i.e. 
once  more,  in  the  direction  of  the  arrows,  first  an  atterminal  (this 
time  ascending),  and  then  an  abterminal  (descending),  phase  of 
the  action  current. 

The  "  nervous  equator,"  i.e.  that  section  of  the  muscle  "  in 
which  would  fall  the  common  centre  of  gravity  of  all  the  nerve- 
endings,  if  these  last  have  a  certain  uniform  equilibrium," 
lies,  in  the  human  forearm,  prettv  close  to  the  elljow.  The 
approximate  equality  of  both  p)]iases  is  remarkable,  from  which 
it  may  be  concluded  "  that  a  decrement  of  the  excitatory  vjave  does 
not  exist  in  the  intact  muscle  ivith  normal  circidation"  and  this  at 
once  explains  why  the  action  current  fails  to  appear  with  any 
certainty  on  tetanising  without  the  rheotome.  Hence  the  ascend- 
ing current  observed  by  du  Bois-Eeymond  in  voluntary  innerva- 
tion of  the  arm  and  les;  is  no  current  of  action  from  the  muscle. 
That  it  is  a  "  secretion  current "  caused  by  the  activity  of  the 
skin-glands  in  the  sense  of  Bequerel's  original  presumption, 
follows  directly  from  the  experiments  of  Hermann  and  Luch- 
singer,  to  be  discussed  below.  The  results  obtained  by  du  Bois- 
Eeymond  on  leading  off  simultaneously  from  a  perspiring  and  a 
dry  hand,  upon  which  the  former  shows  a  descending  current, 
cannot  be  recognised  as  a  valid  objection,  since  they  depend  not 
so  much  upon  the  secretion  present  as  upon  the  secretory  p)i'Ocess 
caused  by  excitation  of  the  nerve.  Like  Bernstein's  experiments 
on  the  negative  variation,  or  current  of  action,  in  frog's  muscle, 
the  experiments  of  Hermann  on  the  human  forearm  give  the 
requisite  opportunity  for  determining  the  velocity  of  excitation 
in  normal  human  muscle.  Its  most  probable  value  is  10—13 
m.  per  sec. 

Matthias  (30)  has  recently  published  a  graphic  record  of  the 
action  current  in  the  human  forearm,  obtained  by  Hermann's 
"  rheotachygraphic  "  method. 

Smooth  muscles,  owing  to  the  much  slower  period  of  all  excita- 
tion phenomena,  are  in  many  respects  more  suited  to  the  investiga- 
tion of  the  action  current  than  striated  muscles,  which  have  hitherto 
been  almost  exclusi^'ely  investigated.  It  is  evident  that  where 
the  wave  of  contraction  is  as  prolonged  as,  e.g.,  in  the  rabbit's 
ureter,  the  phasic  action  current  will  be  directly  demonstrable  in 
a  sensitive  galvanometer  without  applying  to  the  repeating 
method.       In    the  last    resort,  however,  the  number  of  objects 


396  ELECTRO-PHYSIOLOGY 


which  can  be  used  is  unfortunately  limited,  chiefly  because  a 
locally  discharged  excitation  remains  localised  in  most  smooth 
muscular  organs,  and  is  not  propagated  further.  Cardiac  muscle, 
on  the  other  hand,  the  physiological  properties  of  which  entitle  it 
to  some  extent  to  a  middle  place  between  striated  muscle  and 
smooth  muscle -cells,  presents  an  object  peculiarly  appropriate 
to  the  investigation  of  galvanic  phenomena.  As  early  as  1855 
Kolliker  and  H.  Mllller  (31)  observed  the  negative  variation  on 
spontaneous  contraction  of  a  frog's  heart  provided  with  an 
artificial  cross -section,  by  means  of  the  multiplier;  they  soon 
discovered  that  secondary  contraction  may  also  be  obtained 
from  the  same  preparation,  if  the  nerve  of  a  rheoscopic  limb  is 
properly  bridged  across  the  longitudinal  and  transverse  sections. 
Each  systole  is  followed  by  a  twitch  in  the  leg,  occurring  after 
the  auricular,  and  almost  imperceptibly  before  the  ventricular, 
systole.  "  The  twitch  took  effect  sometimes  in  the  lower  part  of 
the  leg,  sometimes  at  the  tarsus  and  toes,  and  was  visible  through- 
out as  a  single  transitory  contraction"  {I.e.  p.  99). 

It  was  presently  found  that  the  same  experiment  produced 
results  in  the  intact  heart  also,  even  when  the  secondary  nerve 
was  laid  transversely  across  the  middle  of  the  anterior  surface  of 
the  ventricle.  The  surface  of  the  uninjured  heart  being  iso- 
electric (as  was  shown  above),  this  last  observation  on  currentless 
cardiac  muscle  shows  once  more  that  the  interpretation  of 
secondary  contraction  as  a  consequence  of  negative  variation,  as 
given  by  du  Bois,  is  not  justified,  but  that  the  electromotive  effects 
(current  of  action)  associated  with  the  activity  of  the  muscle 
must  have  acted  as  a  discharging  stimulus  to  the  nerve  lying 
upon  it.  The  facts  discovered  by  Kolliker  and  Miiller  were 
subsequently  confirmed  and  extended  by  Meissner  and  Cohn 
(32).  Bonders  (33)  repeated  the  experiment  on  secondary 
excitation  from  the  heart  with  the  aid  of  the  graphic  method. 
He  recorded  simultaneously  in  dog  and  rabbit  the  heart-beats 
and  the  contractions  of  a  frog's  leg,  the  nerve  of  which  rested  on 
the  heart.  As  a  rule  each  systole  discharged  a  simple  twitch  in 
the  leg.  Donders  found,  like  Kolliker  and  Miiller  before  him, 
that  the  simple  systole  was  invariably  followed  by  a  secondary 
double  contraction.  It  was  always  possible  to  demonstrate  that 
the  secondary  twitch  appeared  earlier  than  the  -prmiai-y  heart  con- 
traction (about  i^Q  sec.  in  rabbit).    In  a  recently  killed  dog,  whose 


IV  ,  ,.  ELECTROMOTIVE  ACTION  IN  MUSCLE  397 

right  ventricle  was  still  beating  feebly,  the  time-difference  was 
jly  sec.  The  same  was  demonstrated  again  by  Nuel  on  the  frog's 
heart.  On  the  dog  he  was  able,  by  the  physiological  rheoscope, 
to  demonstrate  that  the  contraction  of  the  auricle  is  accompanied 
by  as  marked  an  electromotive  variation  as  that  of  the  ventricle, 
and  that  the  time -difference  between  the  two  electromotive 
processes  corresponds  entirely  with  the  contraction  of  the  two 
cardiac  sections. 

In  order  to  ascertain  more  exactly  the  time-relations  and 
form  of  the  electromotive  variation  (the  "  excitatory  wave ") 
which  accompanies  activity  in  cardiac  muscle,  experiments  were 
undertaken  almost  at  the  same  time  by  Engelmann  (34)  and 
Marchand  (35)  on  the  frog's  heart,  with  Bernstein's  rheotome. 
The  ventricle,  which  had  been  quieted  by  the  removal  of  the 
auricle,  was  stimulated  either  at  its  base  or  apex  by  a  single 
induction  shock ;  whatever  the  situation  of  the  lead-off"  from  the 
surface  of  the  ventricle,  or  the  alterations  in  its  lencrth,  and 
distance  from  the  point  of  stimulation,  the  first  effect  was  invari- 
ably a  current  directed  in  the  heart  away  from  the  seat  of 
excitation.  The  rheotome  is  indeed  superfluous  in  this  connec- 
tion. The  galvanometer  circuit  may  be  permanently  closed  ;  with 
a  sufficient  length  of  tract  led  off,  and  moderate  sensitivity  of 
galvanometer,  the  first  effect  of  the  stimulus  in  every  case  is  a 
deflection  of  the  scale  in  the  given  direction.  Accordingly,  each 
portion  of  the  ventricular  muscle  must,  during  excitation,  become 
temporarily  electromotive  in  a  negative  direction,  which  nega- 
tivity (as  also  contraction,  according  to  Engelmann)  is  propagated 
from  the  seat  of  excitation,  wherever  this  is  situated,  in  all 
directions  through  the  ventricle.  With  the  rheotome  it  may 
further  be  shown  that  on  leading  off  from  the  external  surface  of 
the  ventricle  by  two  points  that  give  no  current  during  rest,  and 
are  at  unequal  distances  from  the  seat  of  excitation,  the  electro- 
motive response  of  the  heart  corresponds  as  a  rule  with  that  of 
normal,  striated,  parallel-flbred  muscle  led  off  from  two  longi- 
tudinal surfaces  ;  i.e.  a  diphasic  variation  usually  makes  its  appear- 
ance, and  that  of  such  a  kind  that  the  point  nearest  to  the  seat 
of  excitation  is  at  first  negative,  and  then  positive,  to  the  more 
distant  point  (Fig.  126). 

In  an  equal  number  of  cases,  however,  the  second  (positive) 
phase   is    wanting,   and    either   the   initial   state   of   indiflerence 


398 


ELECTRO-  PHYSIOLOGY 


recurs,  or  a  weak  after-effect  remains  in  the  direction  of  nega- 
tivity of  the  point  nearest  to  the  seat  of  excitation,  which,  under 
all  conditions,  is  at  first  negative  in  its  reaction.  The  failure  of 
the  second  phase  in  the  last  cases  may  be  explained  on  the  pre- 
sumption that  the  two  variations  follow  so  closely  in  time  as  not  to 
be  clearly  distinguished.  For  with  a  short  tract  led  off  at  normal 
rate  of  propagation,  the  wave  of  negativity  can  obviously  arrive 
at  the  second  electrode  before  it  reaches  its  maximum  at  the 
first  contact.  We  learn  in  detail  from  Engelmann's  experi- 
ments on  the  time -relations  of  the  variation  that  it  seems 
to  begin  at  the  seat  of  excitation  immediately  after  the  impact 
of  the  stimulus,  i.e.  with  no  perceptible  latent  period.  The  stage 
of  increasing  negativity  lasts  on  an  average  for  0*09  sec,  so  that  as, 
according  to  Engelmann's  measurements  on  the  frog's  heart,  the 
contraction   does  not  begm  till   O'l   sec.  later,  the  maximum  of 

negativity    occurs    before    the 
twitch  begins. 

The  continuous  and  fairly 
level  increase  of  negativity  is  very 
remarkable,  showing  as  it  does 
that  the  systole  is  a  simple 
tioitch,  and  not  a  tetanus. 
Contrary  observations  have 
been  made  by  Fredericq  on 
the  dog's  heart.  The  stage  of 
diminishing  negativity  usually 
exhibits  a  much  longer  period, 
and  more  complicated  curve 
of  variation.  When  (as  in  most  cases)  the  current  is  reversed, 
the  E.M.F.  passes  rapidly,  almost  in  a  straight  line,  from  the 
maximum  of  negativity  to  the  maximum  of  positivity,  and  then 
falls  again  gradually  to  its  zero.  The  total  duration  of  the  variation 
is  conditioned  by  many  factors.  In  the  diphasic  variation  Engel- 
mann  estimates  it  at  an  average  of  0'436,  in  the  monophasic  at 
0"211  sec.  The  local  duration  of  negative  electromotive  activity 
may  therefore  be  computed  as  at  least  0'2  sec.  on  an  average. 
As  regards  the  absolute  magnitude  of  the  E.M.F.  of  the  varia- 
tion, it  can  only  be  said  with  certainty  that  it  is  of  the  same 
order  as  that  of  the  artificial  cross -section.  On  leading  off  from 
the    natural    longitudinal    and  fresh    transverse    section    (which 


T^m^^rm^^^mxsti 


Pig.  126. — Diphasic  variation  in  the  ventricle  of 
the  frog's  heart  (rheotome  experiment).  JV", 
negative  ;  P,  positive  phase.  The  time  (in  ^ 
sec.)  is  counted  from  tlie  moment  of  excita- 
tion.    (Engehnann.) 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  399 

must  not  be  too  small),  the  current  is  never  reversed  by  excita- 
tion, only  weakened,  or,  it  may  be,  totally  abolished ;  on  the 
other  hand,  reversal  does  occur  frequently  where  there  is  obvious 
diminution  of  E.M.F.,  and  is  the  more  marked  the  greater  the 
fall  of  potential.  The  velocity  at  which  the  wave  of  negativity 
spreads  over  the  heart  is  reckoned  by  Engelmann  at  20—40  mm., 
but  it  must  be  much  greater  before  the  heart  is  excised,  and  is 
essentially  conditioned  by  temperature.  On  exciting  the  ventricle 
from  the  auricle,  and  in  the  lead-off  from  base  and  apex  of  the 
resting  ventricle  (which  produces  no  current),  the  base  is  at  first 
negative,  afterwards  in  most  cases  positively  active  to  the  apex. 
This  is  seen  in  the  spontaneously  beating  heart,  as  well  as  in 
artificial  excitation  of  the  auricle.  Since  the  negativity  of  the 
base  appears  first  after  the  auricular  contraction  has  passed  by,  it 
cannot  be  due  to  excitation  of  the  auricle,  which  is  also  seen  from 
the  magnitude  of  the  effect,  as  contrasted  with  the  very  small 
deflection  obtained  on  leading  off  directly  from  the  auricles.  It 
must,  therefore,  be  assumed  that  the  excitation  of  the  ventricle 
commences  at  the  base  under  normal  conditions. 

There  is  a  considerable  difference  between  the  results  of 
Engelmann  and  Marchand,  and  those  which  Burdon-Sanderson 
and  Page  (36)  obtained  from  the  frog's  heart  by  the  same  rheo- 
tome  method.  They  investigated  the  action  current  of  the  ven- 
tricle when  separated  from  the  auricle  by  a  ligature,  and  excited 
with  single  induction  shocks  by  means  of  a  (specially  constructed) 
rheotome. 

These  experiments  also  showed  that  each  excited  point  of  the 
heart's  muscle  loas  negative  to  each  p)oint  not  excited,  and  that  the 
process  of  excitation  (i.e.  negativity)  was  equally  distributed  from 
the  seat  of  excitation  on  all  sides,  and  that  with  a  considerably 
greater  velocity  than  Engelmann  had  calculated.  According  to 
the  measurements  of  Burdon-Sanderson  and  Page  the  velocity  of 
the  wave  of  negativity  in  the  frog's  heart  is  about  125  mm.  per 
sec.  at  12°  C,  while  Engelmann  only  reckons  it  as  20—40  mm. 
At  each  point  of  the  ventricle  the  negativity  quickly  reaches  a 
certain  height,  at  which  it  remains  for  a  comparatively  long  time 
(more  than  1  sec),  and  then  slowly  sinks  down  again.  The  total 
duration  of  the  localised  negativity  at  -|-  18°  C.  is  1"6  sec,  at 
-H  12°  C,  2"1  sees,  (on  an  average  0'2  sec. — Engelmann).  These 
time-values  correspond  pretty  exactly  with  the  contraction  period 


400 


ELECTRO-PHYSIOLOGY 


of  the  heart-muscle.  It  is  evident  that  these  facts  coincide  with 
Hermann's  theory,  according  to  which  a  point  of  the  muscle  must 
remain  negative  as  long  as  the  excitatory  (or  contraction) 
process  continues.  Accordingly,  we  should  expect  the  surface 
of  the  ventricle  to  be  isoelectric  during  the  period  of  systolic 
contraction,  as  actually  appears  from  the  experi- 
ments of  Burdon-Sanderson  and  Page. 

If,  in  the  accompanying  Fig.  127,  {a,  x)  is  the 
spot  excited,  {F)  and  (m)  the  two  points  of  the 
ventricle  led  off,'  there  will  follow  on  each  excita- 
tion a  rapid  electrical  variation  (lasting  only  a  few 
Y^o"  sec),  in  the  direction  of  a  current  from  the 
h 


Fio.  127. — a,  b,  Diagrammatic  representation  of  the  electrical  variation  in  an  artificial  cardiac 
contraction  (Burdon-Sanderson  and  Page).  The  continuous  line  corresponds  to  the  process 
of  negativity  at  the  electrode  nearest  the  seat  of  excitation.  The  dotted  curve,  on  the 
contrary,  gives  the  negativity  at  the  more  remote  contact.  The  middle  line  marks  the  time 
in  -^  sec.  (,VN)  corresponds  with  the  negative,  (VP)  with  the  positive  variation  on 
Bernstein's  rheotome. 

seat  of  excitation,  succeeded  by  a  longer  period  (1  —  2"),  during 
which  no  current  is  indicated  by  the  galvanometer;  this  is  followed 
by  an  opposite  phase  of  deflection  (positive  variation)  which  is 
much  weaker  and  more  prolonged  than  the  initial  "  negative " 
variation.  The  interval  separating  the  two  phases  corresponds 
exactly  with  the  duration  of  the  ventricular  contraction,  so 
that  the  one  (negative)  phase  of  the  action  current  marks 
the  beginning,  the  other  (positive)  the  end  of  the  excitation 
(contraction)  of  the  muscle.  The  first  phase  of  the  action 
current  obviously  corresponds  with  the  very  short  period  during 


ELECTROMOTIVE  ACTION  IN  MUSCLE 


401 


which  the  wave  of  negativity  is  already  at  the  leading-off  contact 
nearest  the  seat  of  excitation,  but  has  not  yet  reached  the  more 
remote  contact.  The  subsequent  stage  of  no  current  (and  apparent 
rest)  corresponds  with  the  period  during  which  both  points  led 
off  are  at  the  maximum  of  negativity  (excitation).  The  positive 
phase  at  the  end  corresponds  with  the  moment  at  which  nega- 
tivity is  already  diminishing  at  the  leading-off'  contact  next  the 
seat  of  excitation,  but  still  obtains  unimpaired  at  the  further 
contact. 

Fig.  127,  l,  is  a  graphic  record  of  the  time-relations  of  the 
excitatory  wave  in  the  ventricle  of  the  frog's  heart.      Easy  as  it 


^"X_ 


Fig.  128.— &,  Capillary  electrometer.    (Fredericq.) 


is  with  the  modern,  sensitive  galvanometer  to  demonstrate  the 
P.D.  due  to  spontaneous,  or  artificially  induced,  rhythmical 
activity  of  the  heart,  another  method  that  has  been  much  used  of 
late,  is  still  more  advantageous ;  this  is  the  capillary  electrometer. 
This  instrument,  invented  long  ago  by  Lippman,  but  first  used 
by  physiologists  at  a  much  later  period,  consists  essentially  of  a 
glass  tube,  drawn  out  into  a  fine  capillary  (Fig,  128,  «  and  h,  A), 
the  open  end  of  which  dips  into  a  vessel  (B)  filled  with  dilute 
sulphuric  acid.  The  behaviour  of  the  meniscus  in  the  capillary 
tube  is  observed  with  the  microscope.  If  current  enters  the 
capillary  in  one  or  the  other  direction,  the  surface  polarisation 
will   produce    a   change   in    the   constant   of  capillarity,  with  a 

2  D 


402 


ELECTRO-PHYSIOLOGY 


corresponding  displacement  of  the  mercury  meniscus.  The 
quicksilver  in  the  capillary  responds  even  to  excessively  rapid 
variations  of  the  current ;  but  the  instrument  seems  more 
especially  appropriate  to  experiments  on  the  cardiac  action 
current. 

Marey  (37)  was  the  first  to  use  this  instrument  in  determin- 
ing the  electrical  phenomena  concomitant  with  the  cardiac  systole. 
He  found  that  on  leading  off  from  the  ventricle  of  the  frog;  or 
any  other  animal,  the  electrometer  gave  a  single  oscillation  at 
each  systole.  If  the  entire  heart  is  connected  with  it,  two 
oscillations  can  be  observed  in  the  column  of  mercury.  The  one 
is  referred  by  Marey  to  the  auricular,  the   other  to   the   ventri- 


FiG.  129. — Photographic  record  of  cardiac  action  current,    a,  In  the  Frog's  heart ;  h,  in  the  heart  of 
Tortoise.    Time-marking  in  seconds.    (Marey.) 

cular  systole.  Marey  also  succeeded  in  fixing  these  movements 
by  photographing  the  image  of  the  mercury  meniscus  upon  a 
very  sensitive  plate  moving  at  uniform  speed.  He  concluded 
from  these  experiments  that  there  is  at  each  systole  only  a 
sim2)le  variation  of  current  (Fig.  129,  a  and  h).  Burdon- 
Sanderson  and  Page  employed  this  method  as  a  means  of  con- 
trolling and  completing  their  rheotome  experiments.  There 
appears  to  be  a  fundamental  coincidence  between  the  "  theoretical  " 
curve  (constructed  from  rheotome  experiments)  of  the  variations 
in  the  frog's  heart  excited  at  one  point  of  the  ventricle,  and  that 
projected  on  to  sensitive  paper  by  the  mercury  column  of  the 
capillary  electrometer.  This  appears  directly  from  comparison 
of  the  two  Figs.   172,  h,  and   130,  a.      It  may  be  seen  on  the 


ELECTROMOTIVE  ACTION  IN  MUSCLE 


403 


photogram  that  the  first  "  phasic  action  current "  follows  the 
excitation  at  a  short  interval,  the  apex  being  for  an  infinitesimal 
period,  and  very  rapidly,  positive  to  the  base  of  the  ventricle, 
after  which  there  is  a  longer  interval,  in  which  the  electrometer 
shows  no  deflection ;  then  follows  immediately  the  somewhat 
longer  second  (positive)  phase  of  the  action  current,  when  the 
apex  is  negative  to  the  base.      On  injuring  the  ventricle  at  one 


Fig.  130.— «,  Photograpliic  record  of  action  current  hi  the  Frog's  heart,  with  artificial  excitation  (as 
in  Fig.  127,  «)•  Tlie  interruptions  of  the  dark  line  marlv  the  moments  of  excitation.  6,  Photo- 
graphic record  of  action  cun-eut  after  injuring  the  apex  of  tlie  ventricle.  The  variation 
becomes  monoijhasic.    (Burdon-Sanderson  and  Page.) 


of  the  two  leading-off  contacts,  one  phase  of  course  disappears, 
and  the  variation  becomes  purely  negative,  i.e.  monophasic  (Fig. 
130,  h).  Similar  tracings  of  the  spontaneously  beating  heart 
have  been  photographed  by  other  investigators,  e.g.  Fig.  131, 
A.  D.  Waller, — which  at  first  sight  differs  from  the  results  of 
Sanderson  and  Page,  but  coincides  essentially  with  them.  Here 
we  have  a  simultaneous  record  of  the  contraction  curve  {h,  h), 
and  the  effect  {c,  c)  produced  on  the  capillary  electrometer  by  the 


404 


ELECTRO-PHYSIOLOGY 


current  of  action  in  the  spontaneously  beating  frog's  ventricle.  As 
may  be  seen,  the  first  phase  of  the  action  current  begins  percep- 
tibly earlier  than  the  contraction ;  the  negativity  of  the  former 
(depression  of  the  ndeniscus),  corresponding  with  the  maximum 
P.D.  between  base  and  apex,  is  reached  long  before  the  maxi- 
mum of  contraction,  upon  which  a  reversed  current  ensues  as  the 
second  phase,  when  apex  becomes  negative  to  base.  In  Fig.  131, 
(t)  is  the  time  in  -^jj  sec.  The  capillary  electrometer  is  so 
connected  with  the  base  and  apex  of  the  ventricle,  that  the  effect 
is  downwards,  when  base  is  negative  to  apex. 

Cardiac   response   in   the   tortoise,  and,  as  shown  by  A.  D. 
Waller  and  Reid  (39),  in  warm-blooded  (mammalian)  animals,  is 


Fir;.  131. — Curve  of  contraction  (Ji)  and  action  current  (c)  of  spontaneously  beating 
Frog's  heart.     (A.  D.  Waller.) 

also  analogous  with  that  of  the  frog.  With  artificial  excitation 
of  the  excised  and  already  quiescent  ventricle,  the  proximal 
electrode  is  found  to  be  at  first  negative,  and  immediately  after 
positive,  to  the  distal  electrode,  and  a  diphasic  variation  is  thus 
produced,  in  consequence  of  the  two  phasic  action  currents, 
similar  in  all  respects  to  that  of  the  frog's  heart.  Owing, 
however,  to  the  much  greater  velocity  of  excitation  in  the 
heart  of  warm  -  blooded  animals,  and  the  abbreviated  period 
of  contraction,  the  two  phases  merge  into  each  other,  as  in 
striated  skeletal  muscle.  Fig.  132,  which  is  a  photogram  of  the 
movements  of  the  capillary  electrometer  with  a  normally  beating 
and  artificially  excited  mammalian  heart,  shows  plainly  that  each 
phase  corresponds  with  a  simple  variation,  in  the  sense  of  a  single 
excitatory  wave.      The  capillary  electrometer  also  shows  a  normal 


ELECTROMOTIVE  ACTION  IN  MUSCLE 


405 


diphasic  variation,  during  spontaneous  activity  of  the  mammaUan 
heart,  when  led  off  from  two  points  of  the 
ventricle  (Ijase  and  apex).  But  while  in 
this  case  the  hasc  is  at  first  always  negative 
in  the  frog's  heart,  corresponding  with  the 
invariable  direction  of  the  excitatory,  or 
contraction,  wave  from  base  to  apex — in 
the  mammalian  heart  (although  this  is 
generally  the  case,  as  appears  from  the 
recent  experiments  of  Bayliss  and  Starling, 
40)  there  are  obvious  exceptions,  in  which, 
by  reversal,  either  the  apex  becomes  nega- 
tive earlier  than  the  base  (which  Waller, 
I.e.,  holds  to  be  normal),  or  there  is 
only  a  monophasic  variation.  In  this 
last  case  there  has  usually  been  some 
injury  to  one  of  the  points  led  off,  by 
lesion,  etc.  Bayliss  and  Starling  {I.e.) 
find  that  it  is  possible  by  unequal  warm- 
ing, or  cooling,  of  the  ventricle  in  the 
spontaneously  beating  dog's  heart,  to  reverse 
the  direction  of  the  two  phasic  action 
currents.  It  is  even  sufficient  to  warm 
or  cool  the  inspired  air. 

By  means  of  the  capillary  electrometer  j 
it  is   possible   to   show  the   phasic   action 
current  of  the  heart  in  the  uninjured  body 
of  an  animal,  or  man,  either   by  pushing  fig.  132. -Photographic  record 
two    fine    needle    electrodes    through    the       ^^  '^^"o"  ^"'■'^^"*^  '°  ™^"^- 

malian  heart,  investigated 
with  the  capillary  electro- 
meter. 1.  Spontaneous  beat 
of  the  heart ;  the  first  phase 
corresponds  to  negativity  of 
ajiex  to  base,  the  second  to 
the  reverse  action.  2.  After 
injury  to  apex  of  ventricle. 
3.  After  injury  to  ;base  of 
ventricle.  4.  Excitation 
effects  with  artificial  excita- 
tion of  apex.  5.  Excitation 
effects  with  artificial  excita- 
tion of  base.    (A.  D.  Waller.) 


breast -wall  into  the  ventricle,  and  con- 
necting these  with  the  electrometer,  or  by 
leading  off  from  different  points  of  the 
body-surface  (41).  In  this  case  a  lead-off 
from  the  mouth  is  equivalent  to  leading 
off  from  the  base  of  the  ventricle — a 
lead-off  from  the  rectum,  or  from  a  pos- 
terior extremity,  to  leading  off  from  the 
apex.  In  addition,  the  following  combina- 
tions were  found  (on  man)  to  be  favourable  for  leading-off  (cf. 
Eigs.  133  and  134):— 


Fig.  133. — Schema  of  the  distribution  of  potential  (lines  of  current  diffusion)  arising  from  the 
action  current  in  the  human  heart.    (A.  D.  Waller.) 


ELECTROMOTIVE  ACTION  IN  MUSCLE 


407 


Left  hand  and  right  hand. 
Right  hand  and  left  foot. 
Mouth  and  left  hand. 
Mouth  and  right  foot. 
Mouth  and  left  foot. 


i  FiiT.  134. 


Fic.  134.— Schema  of  distribution  of  potential  caused  by  the  cardiac  action  current  at  the  body- 
surface  in  Man,  and  in  the  Cat.  The  dark  parts  correspond  with  the  lead-off  from  the  apex, 
the  lighter  with  the  lead-off  from  the  base.     (A.  D.  Waller.) 


The  unfavourable  combinations  were  : 

Left  hand  and  left  foot. 
Left  hand  and  right  foot. 
Right  foot  and  left  hand. 
Mouth  and  right  hand. 

These  facts  may  be  explained  by  the  distribution  of  the  lines 
of  current,  or  potential,  in  the  body  (corresponding  with  the  action 
currents  of  the  heart).      In  mammals  the  approximately  median 


408  ELECTRO-PHYSIOLOGY  chap. 

position  of  the  heart  obviates  this  striking  asymmetry  in  the 
distribution  of  differences  of  potential,  which  is  due  to  the  activity 
of  the  cardiac  muscle.  These  experiments  also  yield  di-  or  even 
triphasic  effects  (Fig.  135),  and  according  to  Waller's  earlier 
observations,  the  apex  of  the  heart  is  invariably  negative  at  first, 
corresponding  with  a  basal  direction  of  the  wave  of  excitation. 

Owing  to  the  extraordinary  sensitivity  of  the  capillary 
electrometer,  and  its  very  rapid  reaction,  it  gives  us  a  direct 
reading  of  the  action  current  of  striated  skeletal  muscle,  when 
tetanised.  If  the  capillary  electrometer  is  connected  with  the 
secondary  coil  of  an  induction  apparatus,  each  interruption  or 
closure  of  the  primary  circuit  produces  a  visible  movement  of  the 
meniscus  in  the  capillary  (with  a  proper  adjustment  of  the  coil). 


Fio.  135. — Siniultaueous  record  of  cardiogram  (/;,  /()  and  electro-cardiogram  (e,  e).    (A.  D.  Waller.) 

With  I^eef's  vibrating  hammer,  the  single  oscillations  fuse  into  a 
gray  margin,  which  with  reduced  strength  of  current  seems  to 
blot  out  the  sharp  image  of  the  mercury  meniscus,  and  with 
increased  current  rises  above  it  in  measurable  proportions.  On 
applying  a  battery  current  with  correspondingly  rapid  interrup- 
tions, and  uniform  direction,  the  meniscus  exhibits  a  total 
shifting  in  the  direction  of  the  current.  This,  like  the  oscilla- 
tions, is  smaller  in  proportion  as  the  number  of  interruptions  is 
greater,  and  vice  versa.  In  order  to  detect  the  gray  margin  at 
high  frequency,  along  with  the  total  shifting,  greater  strength  of 
current  is  required  than  at  a  lower  frequency  of  interruption 
(Martins,  42).  This  is  important  in  judging  the  observations 
made  with  the  instrument,  since  a  physiological  process  accom- 
panied by  electromotive  action  can  record  itself  on  the  capillary 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  409 

electrometer  by  a  total  shifting  only,  tinthout  oscillations,  although 
unequal  variations  of  current  are  present  which  fail  to  appear 
in  the  meniscus,  because  the  oscillation  frequency  is  either  too 
high  for  the  existing  E.M.F.,  or  too  low  in  proportion  with  the 
electromotive  frequency.  There  are  two  ways  of  recording  the 
rapid  oscillations  of  the  meniscus  ;  the  beats  may  be  photographed 
on  a  rapidly-moving  sensitive  plate,  which  is  not  difficult  with 
the  present  development  of  instantaneous  photography  (unfor- 
tunately no  methodical  investigation  of  the  action  currents  in 
skeletal  muscle  has  yet  been  undertaken  in  this  manner) :  or 
the  form  and  time-relations  of  the  movements  of  the  meniscus 
may  be  read  off  directly  by  the  stroboscopic  method. 
Martins  {I.e.  p.  590  ff.)  attached  a  paper  flag,  1  cm.  square, 
instead  of  a  writing -point,  to  the  lever  end  of  a  very 
sensitive  electro -magnetic  Pfeil's  chronograph.  If  this  instru- 
ment is  introduced  into  the  circuit  of  the  interrupter,  the  lever 
will  swing  in  the  period  of  the  interrupting  spring.  The  paper 
flag,  at  a  sufficient  frequency,  exhibits  a  broad,  gray  margin  at  its 
upper  and  lower  edges,  while  the  flag  itself  appears  quiescent. 
If  the  oscillating  meniscus  of  the  capillary  electrometer  is 
observed  through  the  lower  or  upper  margin,  its  oscillations 
vanish  altogether,  and  it  appears  sharp  and  fixed  if  it  and  the 
flag  are  vibrating  at  the  same  period.  Now  since  both  oscillations 
are  produced  by  the  same  interrupter,  it  is  obvious  that  the 
mercury  has  no  intrinsic  vibration  period,  but  exactly  repeats 
the  oscillations  of  the  interrupter ;  seeing  that  every  frecpiency 
of  the  latter  (up  to  100  per  sec.)  obliterates  the  vibrations,  i.e. 
gray  film,  of  the  meniscus,  as  previously  visible  in  the 
stroboscope.  It  is  clearly  easy  with  this  method  to  determine 
objectively  the  unknown  frequency  of  periodic  variations  of 
current,  read  off  in  the  oscillations  of  the  meniscus,  if  two  inter- 
rupters are  used,  one  of  which  is  connected  with  the  capillary 
electrometer,  the  other  with  the  stroboscope  in  a  separate 
circuit.  If  the  vibration  period  coincides  in  the  two  interrupters, 
the  oscillations  of  the  meniscus  are  neutralised.  If  they  differ, 
interferences  arise,  from  which  it  is  easy  to  calculate  the  am- 
plitude of  difference  in  vibration  in  the  two  springs  (Martins,  I.e. 
p.  591).  Let  the  rate  of  vibration  in  the  stroboscope  be  18  per 
sec.  If,  instead  of  frequent  oscillations  of  the  meniscus  (which 
can  only  be  counted  artificially),  two  regular  beats  are  observed 


410  ELECTRO-PHYSIOLOGY 


per  second  through  the  margin  of  the  stroboscope,  it  follows  that 
the  interrupting  springs  differ  by  two  beats.  Martins  tested  the 
physiological  applicability  of  the  method  {I.e.  592)  by  leading  oft" 
from  longitudinal  and  transverse  section  of  the  frog's  gastroc- 
nemius to  the  capillary  electrometer  by  unpolarisable  electrodes, 
the  current  of  rest  being  compensated.  On  exciting  the  sciatic 
by  18  break  induction  shocks  per  sec.  the  meniscus  exhibited 
regular  and  visible  oscillations ;  the  stroboscope  was  then  intro- 
duced into  the  primary  circuit  of  the  induction  apparatus,  so  that 
the  flag  vibrated  synchronously  with  the  number  of  stimuli, 
when  the  oscillations  of  the  meniscus  were  extinguished — thus 
proving  that  a  negative  variation  corresponds  with  each  impact  of 
stimulation  in  the  muscle,  an  oscillation  of  the  capillary  meniscus 
with  each  negative  variation.  The  same  effect  is  produced  with 
a  stimulation  frequency  of  30  per  sec.  Unfortunately,  we  have 
thus  far  no  systematic  analysis  of  strychnin  tetanus,  spasm  in 
electrical  excitation  of  the  spinal  cord,  or  the  voluntary  and 
reflex  movements  of  the  frog,  by  this  method.  Loven's  analysis 
(43)  of  voluntary  muscular  contraction  in  the  frog  and  crab  with 
the  capillary  electrometer  yielded  interesting  results,  and  has 
recently  been  confirmed  by  v.  Kries. 

Loven  convinced  himself  that  the  persistent  voluntary  con- 
traction of  the  crab's  muscles,  as  well  as  strychnia  spasms  in  this 
animal  and  the  frog,  are  accompanied  by  definite  and  fairly 
regular  variations  of  current.  The  frequency  of  these  was 
astonishingly  low  (about  8  per  sec.)  That  such  infrequent 
twitches  should  fuse  into  a  persistent  contraction  is  the  more 
remarkable,  since  we  know  that  20  or  more  excitations  per 
sec.  are  required  to  produce  complete  tetanus  on  the  frog  with 
electrical  excitation,  and  according  to  v.  Limbeck's  observations 
34  stimuli  sent  into  the  spinal  cord  can  be  transmitted  to  the 
muscle.  Loven  finds  himself  reduced  to  the  hypothesis  that 
single  voluntary  twitches  travel  more  slowly  than  those  provoked 
by  electrical  excitation.  These  results  tally  with  those  of  Del- 
saux  (44)  (Fig.  136,  a  and  h),  who  only  observed  five  oscillations 
per  sec.  with  the  frog's  gastrocnemius  in  strychnia  tetanus,  on 
the  capillary  electrometer.  The  simultaneous  record  of  change 
of  form  and  electrical  variation  in  muscle  showed  complete  co- 
incidence. 

Since  the  telephone,  like  the  capillary  electrometer,  is  ex- 


ELECTROMOTIVE  ACTION  IN  MUSCLE 


411 


cessively  sensitive  to  a  brief  duration  of  current  (variations  of 
current),  it  was  natural  to  apply  it  to  the  determination  of  the 
current  of  action  in  muscle.  Hermann  (45)  was  the  first  to 
experiment  with  the  telephone,  but  he  failed  to  detect  any 
action  current.  Bernstein  and  Schoenlein  (46),  on  the  other 
hand,  obtained  positive  results  in  1881  with  Siemens'  telephone. 
If  4  to  6  frogs'  gastrocnemii  were  laid  in  working  order  upon  non- 
polarisable  electrodes  (pads),  and  their  nerves  simultaneously 
excited,  a  "  crackling  sound  "  was  plainly  audible  in  the  telephone, 
which  diminished  in  clearness  with  prolonged  excitation.      Further 


Fig.  136.— Photographic  record  of  action  current  in  Frog's  gastrocnemius  in  strychnia  tetanus, 
(c,  c),  curves  of  contraction.    (Delsaux.) 

investigations  were  carried  out  on  the  rabbit.  The  gastrocnemius 
muscles  were  exposed  and  connected  with  the  telephone  by  unpolar- 
isable  electrodes,  or  simple  metal  needles  were  pushed  through  the 
skin  into  the  muscle,  and  thence  led  off  to  the  telephone  (Bernstein, 
47).  In  both  cases  audible  tones  were  obtained,  provided  the 
sciatic  nerve,  which  had  previously  been  divided,  was  tetanised. 
It  was  found,  on  exciting  with  the  acoustic  current  interrupter, 
that  the  number  of  stimuli  might  reach  700  per  sec,  when 
the  note  in  the  telephone,  corresponding  with  the  interrupter,  was 
heard  with  musical  integrity.  Every  note  sung  into  a  second 
telephone  (exciting  telephone  to  sciatic)  was  clearly  distinguish- 


412  ELECTRO-PHYSIOLOGY  chap. 

aljle  from  the  muscle  telephone,  and  had  its  own  characteristic 
pitch.  After  poisoning  with  strychnia  also,  a  deep  singing  tone 
was  clearly  audible  in  the  telephone  at  the  commencement  of  a 
spasm.  Later  on,  Wedenski  (48)  succeeded  in  hearing  the 
action  current  of  a  single  gastrocnemius  in  the  frog,  with  intact 
circulation,  led  off  by  two  needles,  in  the  telephone,  both  with 
artificial  electrical  tetanus,  and  during  voluntary  contraction,  and 
chemical  excitation  of  the  nerve. 

Hesselbach,  who  worked  under  Bernstein's  directions,  pointed 
out  that  even  a  simple  twitch  from  a  single  induction  shock 
produced  an  audible  sound  in  the  telephone ;  which  is  important 
with  regard  to  the  origin  of  the  first  cardiac  bruit,  and  the  nature 
of  systolic  contraction.  To  exclude  reflexes  and  voluntary  move- 
ment, the  sciatic  of  the  rabbit's  thigh  was  divided ;  single  in- 
duction shocks  were  then  led  in  by  two  needle  electrodes  pushed 
into  the  gastrocnemius  muscle.  A  momentary  dull  sound  was  then 
quite  audible  in  the  stethoscope  at  every  twitch,  and  also  when 
all  change  of  form  and  alteration  of  position  in  the  muscle  were 
excluded  by  enclosing  the  ends  in  plaster  of  Paris.  The  "  electrical 
sound "  produced  by  the  concomitant  variation  of  current  must 
be  distinguished  from  the  "  mechaniccd  sound "  that  is  heard 
directly  by  the  ear  in  the  muscle ;  according  to  Bernstein,  how- 
ever, the  two  sounds  coincide  in  time.  Bernstein  concludes  that 
in  listening  to  the  bruit,  or  tone,  of  the  muscle,  we  do  not  hear 
the  process  of  the  twitch,  or  contraction,  but  that  molecular  process 
which  is  electrically  expressed  in  the  action  currents  ;  this,  how- 
ever, postulates  that  the  electrical  variation  as  a  whole  precedes 
contraction,  which  we  have  seen  reason  to  doubt  in  the  previous 
discussion. 

We  remarked  above  that  every  contracted  muscle  must 
be  regarded  as  in  a  state  of  excitation,  while  it  by  no  means 
follows  that  excitation  is  always  accompanied  by  corresponding- 
change  of  form.  From  this  point  of  view,  therefore,  it  seems 
not  impossible  that  electrical  effects  may  arise,  under  certain 
conditions,  without  concomitant  phenomena  of  contraction.  It 
has  long  been  known  that  this  is  the  case  where  there  is  a 
passive  block  in  the  muscular  contraction,  and  Fano  and  Fayod 
(49)  showed  that  in  the  auricle  even  rigid  tension  did  not  pre- 
vent the  development  of  rhythmical  action  currents,  nor  are  they 
quelled  during  the  systolic  stand-still  after  poisoning  with  digi- 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  413 

talis.  We  may  also  refer  to  the  observations  of  Kiihne  (50)  on 
muscles  treated  with  NHg  vapour,  and  strongly  contracted, 
which  still  exhibited  very  striking*  secondary  effects,  when  all 
trace  of  movement  had  been  abolished.  This  occurred  on  makins 
a  new  section,  which  implies  that  there  may  still  be  effective 
waves  of  excitation  in  the  muscle  without  any  subsequent  con- 
traction wave.  Similar  experiments  on  the  adductor  muscle  of 
the  crab's  claw  (Biedermann)  will  be  referred  to  below. 

Fano  and  Fayod  made  the  important  observation  that  the 
"  electrical  pulse  "  of  the  auricle  in  the  tortoise  heart  may  even 
increase  when  immobilised  by  tension ;  this  recalls  the  striking 
effect  of  tension  on  all  muscular  processes,  in  regard  no  less  to 
mechanical  yield  of  work  than  to  thermic  relations.  In  this  con- 
nection, too,  is  the  beneficial  effect  of  tension  in  normal  striated 
muscle  upon  secondary  activity  (51).  Meissner  and  Cohn  observed 
that  with  indirect  excitation  of  the  muscle  the  secondary  (exciting) 
effect  increased  when  the  primary  muscle  was  tetanised  during 
tension.  Even  in  single  twitches  this  is  easily  demonstrated 
on  muscles  in  which  the  excitability  has  perceptibly  diminished. 
The  latter  is  a  sine  qua  non,  because  experience  shows  that  with 
high  excitability  of  the  primary  preparation,  the  secondary  twitch 
will  reach  its  maximum  with  even  low  excitation.  At  a  certain 
stage  of  exhaustion,  e.g.  after  long  heating,  it  is  found  that  the 
capacity  of  giving  secondary  contractions  when  unloaded  is  en- 
tirely lost  by  the  muscle  (gastrocnemius  of  B.  temporaria), 
although  even  a  weak  excitation  from  the  nerve  will  produce 
strong  primary  contractions.  Even  with  strong  excitation,  and 
highly  sensitive  secondary  preparations,  the  latter  are  not  affected. 
In  every  case  the  secondary  efficiency  of  the  primary  heated 
muscle  is  restored  immediately  after  loading,  or  any  kind  of 
tension,  to  disappear  again  as  soon  as  the  strain  is  removed. 
Up  to  a  certain  limit,  the  magnitude  of  the  secondary 
twitch  increases  with  the  load,  but  soon  becomes  maximal, 
and  it  cannot  be  ^:>'/"i7J2«  facie  determined  whether  the  factors 
which  produce  such  a  marked  augmentation  of  secondary 
activity  during  extension  increase  it  still  further  with  constant 
increase  of  loading.  In  the  parallel-fibred  sartorius  also  this 
effect  of  tension  may  be  elegantly  demonstrated.  Since  we 
cannot  doubt  that  the  secondary  action  of  a  muscle  upon  the 
superposed  nerve    of    another  preparation  is  induced   solely  by 


414  ELECTRO-PHYSIOLOGY  chap. 

the  wave  of  electrical  variation  set  up  in  the  latter,  directly,  or 
by  excitation  from  the  nerve,  there  can  only  be  two  alternatives 
as  regards  positive  change  of  sign  in  secondary  action ;  either  the 
conditions  for  neutralisation  of  the  existing  P.D.  by  the  super- 
posed nerve  become  more  favourable,  or  the  magnitude,  form,  and 
velocity  of  the  wave  alter  in  a  direction  more  favourable  to 
excitation  of  the  former.  That  the  first  of  these  possibilities 
does  not  come  into  the  present  consideration  may  be  concluded 
from  the  fact  that  the  experiment  comes  off  as  well  with  regu- 
larly constructed  muscles  as  with  the  usual  nerve-muscle  pre- 
paration. Moreover  it  is  possible,  by  altering  the  position  of  the 
secondary  nerve  on  the  surface  of  the  primary  muscle,  to  render 
the  external  conditions  of  the  discharge  of  secondary  twitches 
during  extension  as  unfavourable  as  possible,  either  by  only 
allowing  it  to  come  into  contact  with  a  very  short  strip  of  the 
extended  muscle,  or  by  placing  it  across,  or  round,  the  muscle, 
which,  however,  in  the  majority  of  cases  has  no  effect  on  the 
result.  Only  the  other  possibility,  therefore,  need  be  considered, 
and  the  magnitude,  form,  and  velocity  of  the  wave  of  electrical 
variation  have  therefore  been  investigated  comparatively  in 
stretched  and  unstretched  muscle.  Heidenhain,  e.g.,  was  the 
first  to  show  that  the  proportion  of  vital  energy  developed  as 
heat  in  contraction  depends  essentially  upon  muscular  ten- 
sion, since,  up  to  a  certain  point,  the  evolution  of  heat  increases 
with  the  loading.  This  suggests  the  idea  that  the  other  factor  in 
the  sum  of  energy,  which  appears  as  electricity  in  the  action 
current  concomitant  with  excitation,  may  be  influenced  in  the 
same  degree  by  tension.  The  experiments  of  Lamansky 
{PJiilgers  Arch.  iii.  p.  193),  who  observed  an  increase  of  the 
negative  variation  in  the  gastrocnemius  with  increase  of  loading, 
would  be  in  favour  of  this  assumption  if  the  exclusive  use  of  the 
irregularly  constructed  gastrocnemius  did  not  suggest  objections 
already  pointed  out  by  du  Bois-Eeymond. 

If  this  theory  is  correct  it  might  be  expected  that  other  data, 
which  are  experimentally  found  to  augment  the  capacity  of  work  in 
the  muscle,  would  also  increase  its  secondary  activity.  The  favour- 
able influence  exerted  under  some  conditions  by  repeated  excitation, 
at  uniform  intensity,  upon  the  mechanical  capacity  for  work  in 
cardiac  and  skeletal  muscle,  where  a  "  staircase  "  is  formed  at  the 
beginning  of  a  series  of  contractions,  has  already  been  referred  to. 


IV  ELECTROMOTIVE  ACTION"  IN  MUSCLE  415 

Electromotive  action  does  therefore,  under  the  same  conditions, 
seem  at  times  to  undergo  a  considerable  augmentation.  If 
properly  excitable  gastrocnemii  of  "  cold  frogs  "  are  employed  as 
primary  preparations,  a  more  or  less  crowded  series  of  twitches 
appears  —  independent  of  loading  or  not  loading  —  with  slow 
rhythmical  excitation  by  the  make  and  break  of  a  primary  in- 
duction coil,  each  of  which  is  also  followed  by  a  secondary  contrac- 
tion, so  that  the  beginning  of  the  primary  series  coincides  with 
that  of  the  secondary  series  of  twitches.  And,  in  conclusion,  if 
primary  twitches  are  summated  into  a  steady,  uniform  tetanus  by 
accelerated  excitation,  this  is  no  less  the  case  as  a  rule  with 
secondary  preparations.  The  primary  sets  up  a  secondary  co- 
incident tetanus.  The  effect  is  quite  different  when  a  warm- 
blooded muscle  is  used  as  the  primary  preparation,  for,  when  it  is 
unstretched,  even  the  strongest  excitation  fails  to  produce  secondary 
twitches.  Thus — apart  from  the  temporary  state  of  excitability 
of  the  preparation — it  depends  solely  upon  the  length  of  the 
interval  which  separates  the  single  stimuli,  whether  or  no  the 
secondary  inactivity  of  the  muscle  continues  during  the  whole 
period  of  incomplete  tetanisation. 

As  a  rule,  when  the  test-nerve  is  placed  upon  the  surface  of  the 
primary  muscle,  the  latter  excites  the  secondary  preparation  after 
a  longer  or  shorter  series  of  ineffective  twitches.  The  secondary 
twitches  are  small  at  first,  but  rapidly  increase  in  magnitude, 
and  may  finally  far  out-top  those  of  the  primary  preparation. 

Since  the  contractions  of  a  warm-blooded  muscle  become 
more  extended  at  a  certain  stage  of  fatigue,  at  which,  more 
particularly,  elongation  takes  up  a  longer  period,  it  may  happen 
that  with  even  a  moderately  rapid  succession  of  single  stimuli, 
the  twitches  of  the  unloaded,  primary  preparation  fuse  into  almost 
constant  tetanus,  the  vigorous  and  perfectly  distinct  secondary 
twitches  alone  expressing  the  internal  changes  of  the  muscle, 
which  correspond  with  each  stimulation-impact ;  the  same  occurs 
also  in  tensely  stretched  muscle.  It  has  already  been  stated 
that  the  period  for  which  the  unstretched  gastrocnemius  muscles 
exhibit  secondary  activity  during  incomplete  tetanus,  is  con- 
ditioned on  the  one  hand  by  the  degree  in  which  the  specific 
muscular  state  induced  by  heat  is  developed,  and  on  the  other  by 
the  intensity  and  number  of  the  successive  stimuli  in  the  time- 
unit.     Here  we  need  only  say  that  the  delay  seems  generally  to 


416  ELECTRO-PHYSIOLOGY 


be  greater,  in  proportion  as  the  induction  current  is  weaker,  and 
the  excitation  intervals,  with  a  given  state  of  excitability,  longer. 
Often  the  secondary  muscle  only  begins  to  twitch  when  the  stimu- 
lation of  the  primary  muscle  has  already  lasted  some  minutes, 
and  when,  owing  to  fatigue,  the  changes  of  form  in  the  latter, 
corresponding  with  the  single  stimuli,  are  hardly  to  be  recognised. 
It  is  natural  to  suppose  that  this  might  be  solely  an  effect  of 
summation  in  the  secondary  nerve,  but  that  is  easily  excluded  by 
applying  the  nerve,  not  at  the  beginning  of  excitation  in  the 
primary  muscle,  but  after  a  greater  or  lesser  number  of  stimuli. 
Without  exception  the  secondary  twitches  appear  in  full  vigour 
as  soon  as  the  nerve  is  brought  into  contact  with  the  primary 
muscle,  showing  that  the  gradual  development  of  activity  in  the 
latter  depends  upon  changes  in  its  substance  produced  by  repeated 
excitation. 

If  in  these  two  cases  it  appears  highly  probable  that  the 
difference  in  the  secondary  action  from  muscle  to  nerve  depends 
upon  the  intensity  of  electrical  action  in  the  former,  in  other 
instances  disparity  of  time-relations,  and  form,  of  the  wave  of 
electrical  variation,  seem  to  be  the  determining  factors.  Above 
all  there  is  the  striking  difference  in  secondary  action  from 
muscle  to  nerve,  when  the  former  is  directly  excited  in  a  variety 
of  ways.  As  a  general  rule  it  is  harder  to  elicit  secondary  con- 
tractions when  the  primary  muscle  is  excited  directly,  than  when 
it  is  excited  from  the  nerve.  Du  Bois-Reymond  in  fact  supposed 
that  there  was  no  secondary  twitch,  if  a  wave  of  excitation  was 
set  up  in  the  sartorius  or  gracilis,  with  a  sciatic  nerve  lying  on  the 
excitable  upper  end  of  the  muscle.  Kiihne  was  the  first  to  show, 
on  the  contrary,  that  the  twitch  produced  by  moistening  the 
fresh  section  of  a  curarised  sartorius  with  a  conducting  fluid 
(which  Hering  proved  to  be  electrical  in  character)  is  peculiarly 
adapted  to  secondary  action,  a  fact  which  only  makes  it  more 
remarkable  that  the  direct  electrical  excitation  of  the  same  muscle 
by  artificial  currents  should  be  so  ineffective  for  this  purpose. 
Kiihne  did,  indeed,  observe  unmistakable  secondary  action 
on  exciting  one  end  of  a  muscle  with  single  induction  shocks,  but 
in  all  these  cases  such  a  strong  current  was  needed  that  special 
control  experiments  were  required  to  exclude  direct  excitation  of 
the  secondary  nerve  by  current  diffusion.  If  a  battery  current 
is  thrown  in   laterally  by  unpolarisable  electrodes  near  one  or 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  417 

the  other  end  of  the  frog's  sartorius,  connected  at  both  ends  with 
the  bones,  the  strongest  excitation  fails  to  produce  any  trace 
of  secondary  action, — notwithstanding  a  marked  twitch  of  the 
primary  muscle  and  favourable  position  of  the  test-nerve, — so 
long  as  both  (thread)  electrodes  are  placed  on  the  continuity  of 
the  muscle,  so  that  the  lines  of  current  must  traverse  it  in  a  more 
or  less  oblique  direction  at  the  point  where  they  enter,  as  well 
as  leave,  the  muscle.  No  alteration  of  this  negative  result  can 
be  detected,  however  much  the  muscle  is  extended.  On  the  other 
hand,  secondary  effects  of  great  intensity  may  regularly  be  seen 
with  weak  excitation  of  the  primary  muscle,  if  the  galvanic 
current  leaves  the  muscle,  at  either  end,  by  the  natural  uninjured 
ends  of  fibres  (51).  It  is  sufficient  to  connect  up  one  electrode 
(kathode)  with  the  stumps  of  bone,  and  to  place  the  other,  by 
which  the  current  enters,  directly  on  the  muscle.  The  secondary 
twitch  occurs  with  one  direction  of  current  only,  while  closure  in 
the  other  direction  is  followed  by  a  vigorous  twitch  of  the  primary 
muscle,  without  excitation  of  the  second  preparation.  It  is  not 
improbable  that  with  simultaneous  and  equal  excitation  of  the 
collective  ends  of  fibres  on  one  side  of  the  sartorius  (as  occurs 
when  the  current  leaves  the  muscle  by  one  or  the  other  end  in 
the  longitudinal  direction  of  the  fibres),  the  wave  of  electrical 
variation  might  be  essentially  distinguished  from  that  which  is 
discharged  with  a  more  or  less  oblique  exit  of  current  through, 
an  electrode  placed  at  the  side  of  the  muscle.  In  every  case, 
how^ever,  we  must  assume  that  the  excitatory  wave  discharged 
by  immersion  of  a  fresh  transverse  section  in  conducting  fluid, 
owes  its  peculiar  aptness  for  secondary  action  to  the  same  condi- 
tion as  the  wave  produced  by  closure  of  an  atterminal  battery 
current,  so  that  the  secondary  inefficiency  of  the  directly  excited 
curarised  muscle  is  only  apparent,  and  produced  by  purely  external 
conditions. 

With  regard  to  these  experimental  results,  it  is  very  striking 
that  the  position  of  the  secondary  nerve  on  the  primary  muscle 
should  have  comparatively  little  influence  on  the  consequences. 
If,  as  it  is  impossible  to  doubt,  this  is  an  electrical  excitation  of 
nerve  by  the  action  current  of  the  primary  muscle,  two  points 
must  be  connected  which  present  a  considerable  difference  of 
potential  at  a  given  moment.  The  most  favourable  position  of 
the  secondary  nerve  is  apparently  that  in  which  it  lies  upon  the 

2  E 


418  ELECTRO-PHYSIOLOGY  chap. 

lower  surface  of  the  sartorius,  parallel  with  the  fibres  of  the  muscle, 
and  as  much  extended  as  possible.  Then,  under  some  conditions, 
the  thinnest  bundle  of  muscle -fibres,  hardly  corresponding  in 
diameter  with  a  frog's  sciatic,  will  suffice,  on  exciting  the  trans- 
verse section,  to  produce  secondary  contraction.  For  the  rest, 
with  moderate  excitability  of  nerve,  hardly  any  position  fails  to 
produce  vigorous  secondary  contraction  of  the  muscle.  Secondary 
excitation  in  which  the  nerve  bridges  the  muscle  at  right 
angles,  has  a  special  interest.  This  is  easily  effected  if  the 
sciatic  of  the  leg,  fixed  on  a  movable  glass  plate,  is  clamped, 
along  with  the  sacral  plexus,  to  a  conveniently  fixed  glass  rod,  and 
applied,  after  moderate  extension,  to  the  inner  surface  of  the 
dependent  sartorius,  or  simply  hung  over  it.  In  the  latter 
case  the  most  vigorous  secondary  contraction  is  found  on  making 
a  double  transverse  section  in  the  sartorius  with  both  ends 
pendent,  or  by  moistening  it  in  the  usual  way  (Kiihne,  5) ;  it 
then  appears  that  the  secondary  activity  of  this  most  regular 
muscle,  on  which  du  Bois'  law  of  the  muscle  current  can  be 
infallibly  demonstrated,  is  independent  of  the  amplitude  of  the 
current  of  rest  to  such  a  degree  that  there  are  actually  no  points 
or  lines  on  the  muscle  excited  from  the  cross-section  which  fail 
to  give  secondary  action.  Even  more  surprising  than  secondary 
excitation  with  the  nerve  laid  across  the  primary  muscle,  is  the 
fact  that  application  to  the  surface  of  the  transverse  section  of 
the  muscle  does  not  abolish  secondary  action,  which  does  not  har- 
monise with  the  prevailing  view  of  the  dependence  of  secondary 
excitation  upon  the  muscle  current  (Kiihne,  I.e.  p.  24  f.) ;  under 
these  conditions,  indeed,  it  might  almost  be  doubted  if  the  wave 
of  electrical  variation  is  really  the  immediate  cause  of  secondary 
excitation.  Kiihne  {I.e.  pp.  27—37),  however,  gave  a  direct  proof 
that  it  is  so,  by  showing  that  the  part  in  contact  with  the 
secondary  nerve  did  not  act  at  the  same  moment  as  that  in  which 
the  primary  excitation  impinged  on  the  muscle  at  another  and 
more  remote  spot,  but  as  much  later  as  was  required  by  the  wave 
of  variation  to  pass  from  its  point  of  origin  to  that  at  which  it  is 
led  off.  The  nerves  of  two  gastrocnemii  were  laid  on  the  sar- 
torius at  some  distance  from  each  other,  and  the  muscle  was  then 
excited  from  one  end.  The  interval  between  the  excitations  of 
the  two  secondary  nerves  was  always  quite  evident,  and  often 
considerable,   although    excessively   fluctuating.       While   in   the 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  419 

most  unfavourable  cases  the  process  excitatory  of  secondary  con- 
traction is  propagated  at  a  velocity  of  25  cm.  per  sec,  i.e.  very 
slowly,  the  velocity  in  other  cases  is  so  great  that  the  methods 
employed  (by  which  velocities  at  2  m.  per  sec.  can  be  estimated) 
were  unable  to  determine  it.  It  appeared  even  from  Bernstein's 
first  experiment  that  the  velocity  of  the  wave  of  electrical  variation 
in  muscle  is  extremely  fluctuating,  and  diminishes  with  comparative 
rapidity  in  the  excised  muscle.  If  the  period  of  the  contraction 
wave  is  any  guide  to  that  of  the  wave  of  variation,  we  might 
recall  the  well-known  waves  of  contraction,  visible  to  the  eye  on 
account  of  their  slowness,  which  appear  more  particularly  in  insect 
muscle,  but  also  under  some  conditions  in  the  freshest  frog's 
muscle,  e.g.,  as  above,  in  the  sartorius  or  adductor  magnus, 
when  mechanically  excited  with  the  point  of  a  needle  (Klihne, 
I.e.  p.  36  f.),  or  as  the  galvanic  wave,  with  strong  battery 
currents. 

With  regard  to  the  question,  which  section  of  the  electrical 
wave  of  variation  is  most  important  in  secondary  excitation,  we 
should  a  priori  be  disposed  to  choose  the  foremost,  i.e.  the 
steepest,  as  most  efficient.  In  any  case  it  is — as  follows  from 
the  evidence  given  above — a  very  short  segment  of  the  excitatory 
wave  which  excites  the  nerve  resting  upon  it. 

In  all  effective  nerve-excitation  (more  particularly  electrical) 
a  certain  rapidity  of  time  distribution  is  implied  in  the  changes 
set  up  by  the  stimulus ;  and  this  appears  in  secondary  excitation 
from  muscle  to  nerve  also,  since  sluggishly-moving  muscles  are 
for  the  most  part  unfitted  to  produce  secondary  excitation  in 
frog's  nerve. 

Matteucci  stated  that  the  secondary  contraction  failed  when 
he  applied  the  frog's  sciatic  nerve  to  the  excited  muscular  mass 
of  the  intestine,  stomach,  or  bladder.  Klihne  confirmed  the  same 
in  the  highly  mobile  ureter  of  the  rabbit ;  nor  could  he  discover 
secondary  action  in  the  striated  muscles  of  Hydrophilus  and 
Astacus,  even  when,  in  the  latter,  the  primary  contraction  of  the 
adductor  claw-muscle  was  produced  by  excitation  of  the  nerve. 
So  again  the  intestine  of  the  tench,  which,  at  the  part  where  there 
are  striated  muscles,  contracts  tolerably  rapidly,  and  almost 
twitches,  with  electrical  excitation.  Klihne  also  found  total 
absence  of  secondary  action  in  the  muscles  of  Emys  europa:a, 
both  in  the  pale  musculi  retrahentes  capitis  coUique  and  the  red 


420  ELECTRO-PHYSIOLOGY  chap. 

muscles  of  the  limbs,  on  applying  electrical  excitation  to  the  former 
directly  (by  puncturing  the  spinal  cord,  or  excising  one  end),  to  the 
latter  from  the  nerve-trunk.  Since  the  tortoise  can  withdraw  its 
head  with  tolerable  rapidity,  and  almost  twitches  its  legs,  at  least 
when  its  nerves  are  artificially  excited  by  induction  shocks,  its  failure 
of  secondary  response  both  to  single  twitches  and  to  tetanus  is 
very  remarkable.  The  extent  to  which  secondary  excitation  from 
muscle  to  nerve  (frog)  is  dependent  on  the  velocity  of  the  excita- 
tion (contraction)  wave  is  elegantly  shown  in  the  heart.  While 
Kiihne  {I.e.)  obtained  only  weak  secondary  twitches  from  the 
ventricle  of  the  beating  tortoise  heart,  which  disappeared  soon 
after  exciting  it,  i.e.  long  before  any  perceptible  diminution  of 
pulse,  the  smaller  but  more  rapidly  beating  frog's  heart  responds 
much  better,  and  the  still  more  rapidly  pulsating  mammalian 
heart  notably  gives  vigorous  secondary  contractions.  On  the 
other  hand,  Kiihne  obtained,  on  exciting  the  nerve,  as  good 
secondary  twitches  and  secondary  tetanus  from  the  red  gastroc- 
nemius, as  from  the  pale  muscles  of  the  rabbit,  although  its 
twitch  is  essentially  more  sluggish. 

J.  V.  Uexklill  (52)  found  that  with  uniform  conditions,  an 
important  factor  in  the  results  of  secondary  excitation  was  the 
point  at  which  the  primary  muscle  (non-curarised  sartorius)  was 
excited.  "  The  simultaneous  excitation  of  muscle-substance  and 
nerve  transversely  to  the  entrance  of  the  latter  into  the  sartorius 
produces  no  secondary  reaction,  while  pure  muscular  excitation, 
like  pure  nerve  excitation,  results  in  secondary  action  under  the 
same  conditions."  Uexkull  showed  by  experiments  on  the 
gracilis  muscle  that  the  occurrence  of  secondary  eff'ects  is  associ- 
ated with  the  coexcitation  of  the  nerve-endings.  Under  certain 
presumptions  {i.e.  a  latent  period  for  the  propagation  of  excitation 
from  the  nerve  end-organ  to  the  muscle,  and  secondary  activity 
of  the  summit  only  of  the  variation  curve  of  the  action  current) 
the  phenomenon  might  be  explained  as  one  of  interference. 
Uexkiill  formulates  the  process  as  follows  :  "  A  stimulus  reaches 
the  nerve  end-organ  and  muscle-fibre  simultaneously,  it  discharges 
a  wave  of  action  in  the  latter  which  would  throw  the  secondary 
limb  into  excitation,  were  it  not  that  the  simultaneously  excited 
end-organ  of  the  nerve  discharged  itself  a  moment  later  upon  the 
muscle.  Hence  instead  of  a  simple  action  wave  there  are  two 
waves  coupled  together.      These  waves  are  inept  for  secondary 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  421 

action,  because  they  are  flattened.  The  whole  j)rocess,  therefore, 
loses  in  crispness,  and  also  in  capacity  for  exciting." 

These  conclusions  leave  no  doubt  as  to  the  influence  which  the 
intensity,  form,  and  distribution  in  time,  of  the  electrical  wave  of 
variation  exert  upon  the  secondary  excitation  of  nerve  and 
muscle.  It  remains  to  consider  the  effect  of  the  time-order  of 
successive  (single)  stimuli  upon  secondary  excitation  and  upon 
electrical  response  of  muscle  in  general. 

Since  secondary  excitation  is  only  a  special  form  of  the  electri- 
cal stimulation  of  a  nerve  still  in  connection  with  its  muscle,  we 
should  a  priori  presume  that  the  same  law  which  dominates  the 
manifestation  of  primary  tetanus,  and  more  especially  its  depend- 
ence on  the  intensity  and  frequency  of  stimuli,  also  holds  good 
for  secondary  tetanus.  Eemembering  further  that  the  electrical 
waves  of  variation  are  not  always  exactly  parallel  with  the 
phenomena  of  contraction,  we  should  not  expect  complete 
parallelism  between  primary  and  secondary  tetanus  (as  actually 
appears  from  the  facts).  Before  the  incapacity  of  many  tetani 
to  produce  secondary  tetanus  was  appreciated,  the  latter  was 
held  to  be  such  an  unfailing  indication  of  primary  tetanus 
that  it  was  appealed  to,  not  merely  in  evidence  of  the  electro- 
motive discontinuity  of  all  tetani,  but  also  in  deciding  be- 
tween contracture  and  tetanus.  It  was  taken  for  granted  that 
a  muscular  movement  which  induces  secondary  twitch,  but  not 
secondary  tetanus,  must  itself  be  a  simple  twitch.  Yet  this  often 
occurs  where  there  is  no  doubt  as  to  the  discontinuity  of  the 
primary  stimulus.  The  effect  in  the  secondary  preparation 
depends  essentially,  as  can  readily  be  demonstrated,  on  the  char- 
acter and  strength  of  the  primary  excitation,  and  therefore  on 
the  intensity  and  frequency  of  the  induction  shocks  sent  into  the 
primary  preparation.  If  the  strength  of  current  is  so  adjusted 
that  the  primary  muscle  is  thrown  into  tetanus,  there  will  be  a 
partial  tetanus  in  the  secondary  muscle  varying  in  length  and 
height,  or  curves  will  be  yielded  which  cannot  in  any  way  be 
distinguished  from  those  sometimes  described  by  the  primary 
muscle  as  "  initial  twitches."  In  rare  cases  we  find  not  merely 
a  secondary  initial  twitch  at  the  beginning  of  primary  tetanus, 
but  also  a  secondary  "  final  twitch "  at  the  end  of  the  excita- 
tion (Schoenlein,  53).  If  the  secondary  initial  twitch  appears  at 
relatively  low  stimulation-frequency,  it  is  mainly  due  to  those 


422  ELECTRO-PHYSIOLOGY  chap. 

changes  in  intensity  and  duration  of  the  action  current  in  the 
primary  muscle,  which  must  be  regarded  as  fatigue  effects,  as  is 
attested  by  the  reappearance  of  secondary  tetanus,  when  the 
primary  muscle  has  had  a  certain  time  to  recuperate.  Thus 
Morat  and  Toussaint  (54)  observed  secondary  initial  twitches, 
with  fatigue  of  the  primary  muscle,  at  a  frequency  of  70—80 
stimuli  per  sec.  Where  fatigue  is  as  much  as  possible  eliminated, 
secondary  tetanus  may  be  kept  up  by  strengthening  the  primary 
excitation,  within  a  wide  range  of  frequency. 

While  the  primary  tetanus  discharged  by  rhythmical  excita- 
tion, electrical  or  mechanical,  does  for  the  most  part  elicit 
secondary  tetanus  also  (though  not  always  coextensive  in  duration), 
in  other  forms  of  artificial  tetanus  this  never  is  the  case  ;  although 
in  favourable  examples  secondary  twitches  may  be  elicited.  As 
we  shall  see  later,  striated  skeletal  muscle  falls,  under  certain 
conditions,  into  prolonged  tetanus  while  the  nerve  is  traversed 
by  a  constant  current  (closure  tetanus),  and  occasionally  after 
the  opening  of  the  circuit  also  (Eitter's  opening  tetanus).  J.  J. 
Friedrich  (55)  found  that  the  secondary  preparation  in  such  a 
case  responded  only,  if  at  all,  by  a  secondary  twitch  at  the 
commencement  of  the  tetanus  under  observation,  never  by  a 
secondary  tetanus.  It  is,  moreover,  remarkable  that  the  effect 
was  much  more  often  absent  in  opening,  than  in  closure, 
tetanus. 

The  tetanus  induced  by  chemical  excitation  of  motor  nerves, 
though  often  pronounced,  is  equally  inefficient  as  regards  second- 
ary tetanus  (Klihne,  I.e.  p.  61  f.)  Salt  tetanus  and  glycerin 
tetanus  produce,  as  Klihne  says,  such  a  large  mechanical  yield  of 
work  from  the  muscle,  that  the  failure  of  secondary  tetanus 
cannot  certainly  be  ascribed  to  weakness  of  muscular  excitation  ; 
it  must  rather  be  owing  to  the  local  mode  of  attack  of  the 
chemical  stimulus,  or  to  its  temporal  relations,  that  the  muscle 
responding  indirectly  to  it  exhibits  such  a  different  reaction. 

This  is  the  more  remarkable  since  every  mode  of  vital  tetanus 
yields  at  most  one  or  more  secondary  initial  twitches,  or  inter- 
mittent secondary  intermediate  twitches,  never  secondary  tetanus. 
Du  Bois-Eeymond  investigated  the  question  "  whether  strychnia 
tetanus,  like  electrical  tetanus,  is  of  an  interrupted  character  "  ; 
he  arranged  his  experiment  so  that  the  test-nerve  was  applied 
to  the  natural  long-itudinal,  and  natural  or  artificial  transverse 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  423 

section  of  the  leg  muscles  of  a  strychninised  frog.  In  favourable 
cases,  "  the  rheoscopic  leg  set  up  a  series  of  weak  twitches  which, 
though  connected,  were  never  very  close  together " ;  it  usually 
remained  quiescent. 

Friedrich  {I.e.  p.  422)  made  the  same  experiment  on  frogs, 
rabbits,  and  guinea-pigs.  Single  twitches,  which  preceded  the 
spasm  of  tetanus  proper,  generally  caused  secondary  twitches. 
An  even  (strychnia)  tetanus,  on  the  contrary — even  if  there  was 
not,  as  frequently,  a  total  failure  of  action — produced  secondary 
twitches  at  the  commencement  only,  never  secondary  tetanus. 
Effects,  corresponding  with  those  observed  by  du  Bois-Eeymond, 
occur  only  when  the  primary  preparation,  instead  of  exhibiting  a 
steady  tetanus,  goes  into  clonic  spasm.  In  other  respects  strychnia 
tetanus  has  a  marked  action  on  the  superposed  nerve.  Strong 
secondary  initial  twitches  accompany  almost  every  spasm  of 
rigor  in  frogs  that  have  been  kept  in  very  dilute  solution  of 
strychnia,  until  for  hours,  and  even  days,  they  will  exhibit 
heightened  reflexes ;  the  nerve  need  only  be  in  contact  with  the 
skin  of  the  leg  in  the  intact  animal  (Kiihne,  I.e.  p.  60). 

Sustained  voluntary  and  reflex  contraction  is  as  little  apt  to 
excite  secondary  tetanus  as  strychnia  spasm.  Harless  was  the 
first  who  tried  to  obtain  secondary  action  from  the  exposed 
gastrocnemius  of  an  otherwise  intact  frog,  during  its  natural 
movements.  Even  when  sustained  contraction  had  been  induced 
in  the  muscle  by  painful  excitation,  Harless  failed  to  dis- 
cover secondary  tetanus ;  there  was  at  most  a  secondary  twitch 
at  the  beginning  of  the  contraction.  Exactly  the  same  occurred 
in  the  reflex  movements.  Another  experiment  of  Harless'  is  in- 
teresting, where  (in  the  frog)  first  the  spinal  cord  and  then  the 
sciatic  plexus,  high  up,  were  electrically  excited.  In  the  former 
case  a  secondary  initial  twitch  only  appeared,  in  the  latter  there 
was  invariably  secondary  tetanus.  In  this  connection  we  may 
quote  the  observations  of  Hering  on  the  contraction  of  the 
diaphragm  in  tetanus,  occurring  in  respiration ;  it  is  not  pos- 
sible to  obtain  secondary  tetanus  of  a  frog's  leg,  with  applied 
nerve,  from  the  contracted  diaphragm,  although  the  same  pre- 
paration falls  into  secondary  tetanus  directly  the  phrenic  nerve  is 
tetanised  by  weak  electrical  excitation,  and  gives  a  tertiary 
twitch  if  the  nerve  of  the  diaphragm  is  divided  high  up  and  laid 
on  the  still  beating  heart,  so  that  the  diaphragm  is  brought  into 


424  ELECTRO-PHYSIOLOGY  chap. 

rhythmical  secondary  contraction  by  the  heart -beat.  A  simple 
method  of  obtaining  a  whole  series  of  secondary  twitches  from 
ordinary  skeletal  muscle,  reflexly  excited,  is  that  given  by  Kiihne 
(I.e. -p.  63):  a  lizard's  tail,  amputated  and  curled  up,  produces 
vigorous  excitation  in  the  nerve  of  a  frog's  leg  brought  into 
contact  with  it.  Natural  rapid  contractions  do  accordingly 
possess  considerable  secondary  efficiency. 

The  telephone,  as  a  proof  of  the  discontinuous  electrical 
wave  of  variation  in  muscle  in  natural  tetanus,  presents  great 
advantages  over  the  rheoscopic  test.  Bernstein  and  Schoenlein 
(56)  heard  "a  deep,  singing  tone  of  unmistakable  clearness"  on 
the  strychninised  rabbit  at  tlie  outset  of  spasm.  Later  on 
Wedenski  (48)  organised  a  whole  series  of  experiments  in  this 
connection.  At  each  energetic  natural  contraction  of  triceps 
femoris  in  the  frog,  he  succeeded  in  hearing  a  perfectly  distinct 
murmur  (aspiration)  in  the  telephone.  The  same  effects,  only 
more  intense  and  persistent,  were  heard  during  spasms  produced 
by  destruction  of  the  spinal  cord.  Wedenski  also  experimented 
on  himself  (by  pushing  two  needles  into  his  biceps  brachii),  as 
well  as  on  toads,  dogs,  and  rabbits.  The  animals  were  either 
poisoned  with  strychnia,  or  tetanised  from  the  cord.  In  all  these 
experiments  a  hardly  definable,  but  deep  and  regular  murmur  or 
aspiration,  was  heard,  like  the  sound  of  a  distant  waterfall.  If 
the  arm  is  held  out  for  a  considerable  time,  the  murmur  becomes 
weaker,  and  eventually  dies  out  (fatigue).  The  sound  is  deep, 
but  its  pitch  indeterminable ;  the  attempt  to  determine  it 
synthetically  by  artificial  measures  gave  negative  results,  since 
excitations  of  8—20  beats  per  sec.  yielded  electrical  tones  of 
a  perfectly  different  character  from  the  murmur  heard  in  the 
telephone  in  voluntary  contraction. 

However  completely  the  telephone  may  attest  the  oscillatory 
nature  of  the  electrical  processes  in  voluntary,  active  muscle,  it 
has  the  great  defect  of  giving  no  determination  of  frequency  of 
variation. 

The  cause  of  the  failure  of  secondary  tetanus  in  the  above- cited 
instances  has  been  the  object  of  repeated  investigation.  Du  Bois- 
Eeymond  (1)  pointed  out  the  relative  instability  of  voluntary  and 
strychnia  tetanus.  Supposing  the  contractions  of  the  different 
groups  of  fibres  in  a  muscle  not  to  occur  simultaneously,  it  is 
conceivable  that  the  electrical  variations,  led  off  externally,  might 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  425 

produce  mutual  disturbance  or  neutralisation,  so  that  the  effect 
on  the  superposed  secondary  nerve  would  be  abolished,  which  is 
not  the  case  when  with  rhythmical,  artificial  excitation  of  the 
nerve  the  collective  elements  respond  in  the  same  phase  with  a 
uniform  reaction.  More  recently  Hering  (55)  and  Briicke  have 
formulated  a  similar  theory,  and  the  latter  expresses  the  relation 
figuratively  by  contrasting  the  artificial  excitation  from  the  nerve 
as  a  "  volley,"  with  the  irregular  discharge  or  "  platoon  fire  "  from 
the  central  organ.  The  inefficacy  of  the  primary  tetanus  pro- 
duced by  chemical  excitation  of  the  nerve,  with  regard  to  second- 
ary action,  may  be  explained  in  the  same  manner.  "  If  we 
imagine  the  secondary  action  of  the  muscle  to  proceed,  not  from 
a  single  muscle-fibre,  but  always  from  groups  of  fibres,  and  that 
in  every  such  group  the  waves  of  variation  run  parallel  with 
each  other  in  no  definite  order,  we  have  the  conditions  which 
result  in  negation  of  the  external  effect,  since  the  neutralisation 
of  the  differences  in  electrical  potential,  which  are  the  sole  cause 
of  all  secondary  excitation,  proceeds  in  the  muscle  from  one  fibre 
to  the  other,  from  each  negative  point  of  the  one  to  the  less 
negative,  or  positive,  of  the  adjacent  fibre"  (Kiihne,  50).  Hence 
it  only  remains  to  find  the  rationale  for  the  early  expiration  of 
secondary  tetanus,  or  appearance  of  the  secondary  initial  twitch, 
with  the  rhythmical  "  volley  "  of  electrical,  or  mechanical,  excita- 
tion. This  presents  no  difficulty,  provided  the  conditions  of  the 
appearance  of  the  primary  initial  twitch,  and  more  particularly 
its  dependence  on  the  intensity  and  frequency  of  the  tetanising 
stimuli,  are  kept  in  mind.  According  to  the  capillary  electro- 
meter and  telephone,  the  intensity  of  the  electrical  variations  of 
the  muscle  declines  very  rapidly,  and  in  each  case  much  earlier 
than  the  contraction.  If  in  addition  to  this  the  stimulation- 
frequency  is  considerable,  we  have  sufficient  ground  for  the  brief 
duration  of  the  secondary  tetanus. 

There  is  yet  another  factor  to  which  Kiihne  {I.e.  p.  68)  first 
drew  attention.  A  striated  muscle  notably  presents  no  physio- 
logical entity,  since  at  least  two  functionally  distinct  kinds  of 
fibres  enter  into  its  composition.  It  only  requires  a  different 
tempo  in  the  rate  of  alterations  of  velocity  in  the  dark  (red), 
slowly  reacting  fibres  to  that  of  the  quick,  light  fibres,  to  produce 
such  interference  between  the  waves  of  variation,  that  no  differ- 
ence of  electrical  potential  at  the  surface  remains  to  excite  the 


426  ELECTRO-PHYSIOLOGY  chap. 

superposed  nerve.  We  have  in  fact  observed  that  the  light 
fibres  are  much  more  quickly  fatigued  than  the  dark  fibres. 

With  regard  to  the  last  point  also,  it  can  hardly  be  supposed 
that  the  wave  of  variation  produced  at  one  end  of  a  muscle 
with  parallel  fibres,  reaches  every  fibre  at  the  same  phase,  and  in 
this  we  ought  to  find  an  explanation,  not  merely  of  the  vigorous 
excitation  experienced  by  a  nerve  laid  at  right  angles  across  a 
strong  bundle  of  such  fibres,  but,  still  more,  of  the  otherwise 
hardly  intelligible  secondary  activity  of  the  rectangular  cross- 
section. 

It  is  remarkable  that  during  life  the  contracting  muscles 
apparently  exert  no  secondary  action  upon  the  nerves  lying 
between  them.  Hering  showed  indeed  that  the  twitches  of 
the  diaphragm  (cat)  first  observed  by  Schiff  and  not  explained 
subsequently,  which  are  isochronous  with  the  beat  of  the  heart, 
are  produced  by  the  contact  of  the  phrenic  nerve  with  the 
beating  heart.  No  other  instance  is  known,  and  it  is  easier 
to  demonstrate  that  under  the  most  favourable  conditions,  no 
secondary  excitation  of  extra-muscular  nerves  in  sihc  results 
from  muscles  foreign  to  them.  If  the  sciatic  nerve  is  cut 
close  below  the  departure  of  the  branches  to  the  thigh,  the 
muscles  of  the  leg  and  foot  are  quiescent,  even  with  strong 
tetanising  excitation  of  the  same  plexus,  although  the  nerve  to 
the  leg  is  embedded  between  the  much-contracted  thigh  muscles 
(Kiihne).  It  is  easy  to  show  that  this  cannot  be  referred  to  the 
short-circuiting  of  the  action  current  within  the  surrounding 
mass  of  muscle.  Kiihne  always  obtained  secondary  action  when 
he  packed  the  nerve  of  a  frog's  leg  in  the  thigh,  after  removing 
the  bone,  and  then  excited  the  sciatic  plexus,  and  it  is  well  known 
how  little  other  moist  bodies,  serving  as  a  deriving  circuit,  are 
able  to  hinder  secondary  action.  Thick  layers  of  filter-paper,  or 
packing  the  primary  muscle  and  secondary  nerve  on  all  sides  in 
the  viscera  of  a  female  frog,  produce  no  disturbance  of  secondary 
excitation  effects.  That  in  secondary  inexcitability  of  the  nerves 
in  situ  there  is  "  a  special  adjustment  of  the  muscular  and 
nervous  activity,  which  really  accomplishes  much  more  than  is 
demanded  by  the  natural  conditions,"  seems  evident  from  the  fact 
detected  by  Kiihne,  that  even  a  slight  dislocation  of  the  nerves 
lying  between  the  muscles  of  the  thigh,  or  their  simple  exposure, 
suffices  to  call  out  the  absent  secondary  effect,  while  on  closing 


IV  ELECTROMOTIA^E  ACTION  IN  MUSCLE  427 

the  wound  it  disappears  again.  With  Kllhne  we  must  recognise 
"  that  the  nerves  m  situ  are  protected  against  the  apparently 
dangerous  vicinity  of  the  muscles  between  which  they  course,  by 
the  characteristic  properties  of  the  latter,  which  forbid  them 
any  activity  relatively  to  each  other  beyond  the  hindering  of 
neutralisation  of  the  myoelectric  potential  in  the  tract  through 
which  the  nerve  passes  "  (which  might  perhaps  be  referred  to  the 
principle  of  interference,  or  exclusion  of  the  summated  action  of 
the  waves  of  variation). 

After  Hering  had  determined  that  the  muscle  can  be  excited 
by  its  own  demarcation  current,  it  was  naturally  presumed  that  it 
must  also  be  possible  to  produce  secondary  excitation  from  muscle 
to  muscle.  In  spite  of  many  attempts  the  first  experiments  to 
this  end  were  totally  ineffective,  since  neither  on  partial  excita- 
tion of  a  muscle  were  its  fibres  collectively,  nor  on  total  excitation 
were  the  adjacent  muscles,  coexcited.  Klihne  was  the  first  who 
succeeded  in  obtaining  secondary  (pre-systolic)  excitation  of  the 
frog's  sartorius  by  the  action  current  of  the  slowly  beating  tortoise 
heart,  which,  as  we  have  shown,  is  characterised  by  its  secondary 
inefficiency  towards  the  nerves  of  the  frog.  This  shows  once  more 
the  extent  to  which  secondary  excitation  depends  on  the  time-rela- 
tions of  the  current  of  action  :  the  more  slowly  reacting  muscle 
corresponds  better  with  a  slower  wave  of  variation,  while  the 
quickly  reacting  nerve  is  best  excited  by  a  rapid  variation.  Later 
on  Kiihne  succeeded,  under  certain  special  conditions,  in  producing 
secondary  excitation  from  muscle  to  muscle  on  the  skeletal  muscle 
of  the  frog  also. 

While  he  never  succeeded  in  bringing  a  sartorius  into  con- 
traction by  applying  it  to  another  directly,  or  indirectly,  excited 
muscle,  without  pressure,  the  effect  never  fails  when  the  muscles 
are  partially  pressed  down  upon  one  another  (Klihne,  57).  Under 
these  conditions  one  muscle  will  produce  secondary  excitation  in 
a  whole  series  of  other  muscles,  brought  together  by  the  ends, 
under  pressure.  Indirect  excitation  of  the  primary  preparation 
from  the  nerve  is  in  such  a  case  effectual,  even  when  the  secondary 
excitation  fails  in  a  superposed  nerve.  This  is  especially  true  in 
regard  to  clonic  and  tonic  glycerin  spasms,  which  fail  to  effect  any 
but  very  weak  excitation  in  the  secondary  nerve-muscle  prepara- 
tion. This  alters,  however,  as  soon  as  the  primary  muscle  is  parti- 
ally pressed  down,  when  the  secondary  nerve,  lying  in  the  proximity 


428  ELECTRO-PHYSIOLOGY  chap, 

of  the  seat  of  pressure,  is  vigorously  excited  by  glycerin  excitation 
of  the  primary  nerve.  The  same  occurs  when  a  second  sartorius  is 
introduced,  with  the  press,  between  the  first  and  the  nerve  to 
the  leg.  On  the  other  hand,  the  strongest  excitation  induced 
by  ammonia  in  the  primary  muscle  is  incapable  of  transfer  to 
the  secondary  nerve,  or  to  a  second  muscle.  Direct  electrical 
excitation  of  the  primary  muscle,  which  is  otherwise  little  fitted 
to  effect  secondary  excitation  in  a  superposed  nerve,  is  in  the 
pressed  muscle  extremely  efficacious  in  secondary  excitation  of 
the  accessory  muscle,  even  in  the  case  in  which  the  current  is 
directed  in  the  muscle  from  tendon  to  surface.  Total  contraction 
towards  a  localised  stimulus,  as  well  as  a  tendency  to  sustained 
tetanic  shortening,  is  characteristic  of  each  compressed  muscle. 
The  first  appearance  is  easily  explained  by  the  secondary  action 
from  fibre  to  fibre,  and  the  two  work  together  in  producing  the 
extreme  sensitivity  of  the  partially  compressed  muscle :  "  At 
each  impact  of  stimulation,  when  the  normal  muscle  only  reacts 
almost  imperceptibly  with  a  couple  of  marginal  fibres,  the  com- 
pressed muscle,  being  prevented  from  twitching  in  bundles, 
shrinks  together  simultaneously  throughout  its  breadth,  and  while 
the  former  can  scarcely  move  a  small  load,  the  latter  lifts  a  heavy 
weight,  raising  it  while  still  in  tetanus  to  a  considerable  height, 
and  holding  it  there  for  several  seconds "  (Kiihne).  With 
regard  to  the  constancy,  or  discontinuity,  of  the  electromotive 
process  during  tetanus  contraction  of  the  compressed  muscle,  it  is 
important  to  note  that  in  contrast  with  the  secondary  inefficiency 
of  the  closure  and  opening  tetanus,  the  strongest  secondary  tetanus 
may  result,  if,  with  excitation  of  the  primary,  partially  compressed 
sartorius  by  the  battery  current,  the  secondary  nerve  is  laid  on 
that  portion  of  the  muscle  which  projects  from  the  press.  It 
appears  from  this  that  the  tetanus  outlasting  excitation  in  the 
pressed  muscle  must  not  be  taken  for  contracture,  but  as  regards 
electromotive  response  is  to  be  viewed  as  a  discontinuous  pro- 
cess, similar  to  that  of  the  true  oscillating  tetanus  with  rhythmical 
excitation. 

If  any  doubt  still  remains  that  there  is  in  all  these  cases 
electrical  coexcitation  of  the  accessory  muscle  (or  nerve),  it  is 
removed  by  the  fact  that  the  thinnest  sheet  of  a  flexible  non- 
conductor, or  metallic  intermediate  layer  (gold  leaf),  prevents 
the   appearance   of  the   secondary  excitation.      Kiihne,  moreover, 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  429 

has  succeeded,  though  rarely,  in  producing  secondary  excitation 
from  muscle  to  muscle  by  means  of  electrical  conductors  (salt 
clay),  an  experiment  from  which  du  Bois-Eeymond  obtained  the 
first  indisputable  proof  that  Matteucci's  twitch  depended  on 
electrical  processes  in  the  primary  muscle.  As  regards  the 
cause  of  the  remarkable  effect  produced  by  compression  of  the 
muscle  on  its  secondary  activity,  some  light  is  obtained  from  ex- 
periments recently  carried  out  re  effect  of  dehydration  from 
desiccation  (Biedermann,  58). 

If  dead,  skinned  frogs,  or  even  parts  of  such,  are  exposed  freely 
in  the  air  for  some  hoars,  at  not  excessive  external  temperature, 
they  take  on  very  remarkable  properties  at  a  certain  stage  of 
desiccation,  which  distinguish  them  in  a  marked  degree  from 
normal  muscles,  even  at  a  high  state  of  excitability.  Here,  as 
in  partially  compressed  muscles,  every  stimulus,  however  localised, 
produces  an  extremely  vigorous  and  also  protracted,  persistent 
shortening  of  the  ivhole  muscle  directly  affected,  and  in  many 
cases  of  other  accessory  muscles  also,  so  that  energetic  movements 
and  changes  of  position  result  in  these  extremities,  often  producing 
an  impression  of  reflex  or  voluntary  movements.  The  excitability 
is  not  seldom  heightened  to  such  a  degree  that  even  the  least 
shake,  such  as  lifting  the  dish  containing  the  skinless  remains  of 
the  frog,  sufiices  to  throw  certain  muscles  into  persistent  contrac- 
ture ;  a  gentle  touch  of  the  dry  surface  always  produces  this 
result.  It  is  easy  to  demonstrate  that  this  reaction  in  dried 
muscle  is  principally  due  to  dehydration  of  the  superficial  layers 
of  fibres,  by  moistening  every  point  found  to  be  sensitive 
to  mechanical  or  electrical  stimulation  with  physiological  salt 
solution,  on  which  the  characteristic  effect  soon  disappears 
permanently,  although  it  may  still  be  elicited  in  other  dry 
parts. 

If  an  isolated  sartorius  at  the  right  stage  of  desiccation 
is  placed  upon  a  glass  dish  with  the  non-fasciculated  inner  side 
turned  downwards,  a  series  of  effects  can  be  produced  by  the 
most  simple  methods,  which  mark  off  such  a  preparation  distinctly 
from  the  normal  muscle,  however  excitable.  Excitation,  with  a 
needle,  of  the  fibres  adjacent  to  the  inner  or  outer  margin,  at  any 
point,  results,  as  a  rule,  in  vigorous  contraction  of  the  whole 
muscle,  so  that  there  is  no  doubt  that  the  excitation  which  was 
originally  limited  to  a  few  primitive  fibres  communicates  itself  in 


430  ELECTRO-PHYSIOLOGY  chap. 

some  way  or  other  to  the  remainder.  Here  again,  after  the 
shortest  excitation,  the  contraction  is  prolonged,  and  of  a  tetanus 
character  analogous  to  that  of  compressed  muscle. 

Total  excitation  of  the  entire  sartorius  also  occurs  at  the 
beginning  of  desiccation,  if  the  muscle  is  partially  split  longi- 
tudinally (Kiihne's  "  bifurcate  experiment "),  one  half  only  being 
directly  or  mechanically  excited.  Both  halves  are  then  seen  to 
contract  simultaneously,  and  since  the  experiment  also  succeeds 
when  the  connecting  bridge  of  muscle  is  barely  ^  cm.  long,  the 
purely  mechanical  action  of  the  directly  excited  bundle  of  fibres 
upon  the  adjacent  half  could  hardly  be  an  adequate  stimulus 
within  the  short  tract  in  which  it  is  effective.  Thus  there  is 
almost  complete  coincidence  between  the  response  of  a  dried  and 
isolated,  and  that  of  a  fresh,  partially  compressed  sartorius. 

This  also  appears  from  experiments,  in  which  the  excitation 
is  transferred  from  one  sartorius  to  a  second  in  close  juxtaposi- 
tion. If  two  suitable  muscles  are  laid  together  by  the  broad,  unin- 
jured, pelvic  ends,  so  that  the  dry  outer  surfaces  are  coextensive 
for  about  1  cm.,  the  two  muscles  react  as  a  whole — as  an  excitable 
mass,  cohering  in  every  part,  and  conducting  in  all  directions. 
Not  merely  is  each  excitation  of  the  one  muscle,  discharged  by 
any  localised  stimulus,  propagated  from  fibre  to  fibre  in  the 
same  muscle,  but  the  primarily  excited  muscle  twitching  as  a 
whole,  throws  the  other  also  into  secondary  excitation. 

It  was  shown  that  desiccated  muscles  behave  exactly  like 
compressed  muscles,  i.e.  they  respond  to  a  short,  single  stimulus, 
not  as  under  normal  conditions  by  a  rapid  twitch,  but  by  falling 
with  great  regularity  into  prolonged  contracture,  or  a  state  of 
persistent  disquietude.  In  the  latter  case  the  secondary  muscle 
may  be  seen  to  follow  each  movement  of  the  primary  with  the 
utmost  exactness  in  every  detail,  as  if  the  excitation  were 
directly  transmitted  from  one  preparation  to  the  other.  The 
nature  of  secondary  excitation  from  drying  muscle  to  superposed 
nerve  is  also  remarkable,  since  it  tells  in  favour  of  the  dictum 
that  a  rhythmical,  discontinuous  change  of  state  corresponds  with 
the  seemingly  continuous  contracture,  after  a  single  short  excita- 
tion. If  the  nerve  of  a  sensitive  preparation  is  laid  longitudinally 
upon  an  isolated  sartorius  undergoing  desiccation,  the  leg  falls  at 
each  contracture  into  gentle  secondary  tetanus, — without  reference 
to  the  nature  of  the  stimulus,  whether  discontinuous  excitation,  or  a 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  431 

single  short  stimulus.      Compressed  muscle,  according  to  Klihne 
(supra),  exhibits  a  similar  reaction. 

The  complete  uniformity  of  response  between  desiccated  and 
compressed  muscle  leads  to  the  conjecture,  that  the  striking 
tendency  to  secondary  excitation  in  both  cases  must  be  ascribed 
to  one  and  the  same  cause,  i.e.  dehydration,  produced  in  the  one  in- 
stance by  slow  evaporation,  in  the  other  by  strong  pressure.  It  is 
of  little  consequence  that  the  alteration  which  produces  second- 
ary excitation  concerns  the  entire  muscle  in  the  one  case,  and 
only  a  larger  or  smaller  section  of  it  in  the  other.  Klihne  him- 
self remarks  opportunely  that  "  the  muscle  comes  out  of  the 
press  as  if  it  had  been  desiccated,"  and  calls  attention  in  another 
place  to  the  "  dry,  dull  appearance  "  of  the  pressed  and  flattened 
strip  of  muscle,  which  gives  the  same  constant  response  even  after 
removal  of  pressure,  so  that  cdteration  of  the  muscle-substance 
must  be  held  the  true  cause  of  secondary  activity.  In  regard  to 
excitability  also,  there  is  a  general  conformity  between  com- 
pressed and  desiccated  muscle,  since  in  both  cases  it  appears  per- 
ceptibly heightened.  This  is  indeed  to  a  much  greater  degree 
the  case  with  the  slow  loss  of  water  by  evaporation  than  in 
pressure,  in  which  Kiihne  only  succeeded  in  demonstrating  an 
unmistakable  rise  of  excitability  in  the  compressed  tract  at  the 
beginning,  while  later  on,  in  spite  of  marked  secondary  action,  it 
showed  a  significant  decrease  of  response.  For  the  rest  the 
increase  of  excitability  cannot  in  itself  be  regarded  as  the  sole 
cause  of  secondary  excitation,  since  it  is  easy  to  show  that  a  much 
more  significant  rise  of  excitability  produced  in  another  way 
(effect  of  !N"a2C0g  solutions)  does  not  enable  the  muscles  to  react 
on  one  another  as  described.  Just  as  little  can  it  be  due  to  the 
altered  time -relations  of  the  excitation,  since  poisoning  with 
veratrin,  which,  of  course,  throws  the  muscle  into  a  state  in 
which  it  falls  into  sustained  contracture  at  the  slightest 
stimulus,  would  then  induce  secondary  excitation  from  muscle 
to  muscle,  which  never  is  the  case.  An  important  point  appears 
on  the  contrary  from  the  fact  that  the  antagonistic  contact 
of  the  preparations  is  incomparably  more  intimate,  when  the 
contiguous  surfaces  are  at  a  certain  degree  of  desiccation.  This 
may  also  have  some  application  in  individual  muscles,  where  the 
single  primitive  fibres  lie  in  closer  juxtaposition,  in  proportion 
as  the  muscle  loses  water.       Still  it  is  striking  that,  notwith- 


432  ELECTRO-PHYSIOLOGY 


standing  the  undoubted  difference  of  water-content  in  the  super- 
ficial and  deeper  layers  of  fibres  in  the  muscle,  the  transfer  of 
excitation  does  not  seem  to  be  confined  to  the  former,  although 
the  direct  excitation  of  the  moister,  non-fasciculated  inner  side 
is  less  certain  to  produce  secondary  excitation  of  the  muscle  than 
stimulation  of  the  dry  outer  surface.  This  seems  to  indicate  that 
the  dry  layers  of  fibres,  which  are  the  most  excitable,  may 
perhaps  be  distinct  from  the  others  in  yet  another  characteristic 
{i.e.  more  pronounced  electromotive  activity).  In  any  case  many 
factors  combine  to  produce  this  response  of  desiccated,  or  com- 
pressed, muscle. 

Langendorff  (59)  has  recently  made  some  interesting  observa- 
tions, in  the  frog,  on  phenomena  analogous  to  those  of  drying 
muscle,  after  subcutaneous  injection  of  glycerin ;  these  effects 
seem  equally  to  be  due  to  a  secondary  excitation  from  muscle  to 
muscle  caused  by  dehydration.  If  1'5  — 2  cc.  glycerin  is  in- 
jected under  the  skin  of  the  back  of  a  curarised  frog,  vigorous 
and  sustained  contractions  appear  after  some  time  at  each  excita- 
tion, not  merely  in  the  same,  but  also  in  adjacent  muscles,  similar 
to  those  which  may  be  observed  in  desiccated  preparations,  and 
doubtless  to  be  interpreted  in  the  same  manner. 

III. — Positive  Variation  of  the  Muscle  Current 

Hering  distinguishes,  in  addition  to  the  "  action  current "  of 
Hermann,  due  to  a  "  down "  change  at  a  led-off'  part,  a  second 
kind  of  action  current  caused  by  an  "  up  "  change  of  a  led-off 
point,  without  any  necessary  "  down  "  change  at  the  other  lead- 
off.  If  this  should  happen  in  the  case  of  a  muscle,  it  would 
obviously  give  rise  during  tetanisation  to  a  positive  instead  of  a 
negative  variation  of  the  demarcation  current,  due  to  increased 
positivity  of  the  uninjured  longitudinal  surface,  associated  with 
upward  modification.  And  in  point  of  fact,  certain  recent 
observations  seem  to  substantiate  this  theoretically  possible 
event.  Gaskell  (60),  in  the  first  place,  observed  a  pronounced 
positive  variation  upon  the  cardiac  muscle  of  the  tortoise  during 
excitation  of  the  vagus  nerve.  We  subsequently  succeeded  in 
demonstrating  a  similar  effect  upon  the  adductor  muscle  of  the 
crab's  claw  during  indirect  electrical  tetanisation.  As  a  result 
of  a  prolonged  series  of  experiments  upon  the  innervation   and 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  433 

physiological  properties  of  cardiac  muscle,  Gaskell  came  to  the 
conclusion  that  cardiac  (and  all  other)  tissue  is  supplied  by  two 
kinds  of  functionally  opposed  nerve-fibres,  one  of  which  (motor 
or  accelerator  nerves)  he  terms  "  katabolic,"  inasmuch  as  their 
presumable  action  is  to  bring  about  a  destructive  change,  while 
the  other  (inhibitory  fibres)  he  terms  "  anabolic,"  because  the 
alterations  to  which  they  give  rise  are  of  a  constructive 
( =  assimilatory)  character.  Just  as — in  accordance  with  this 
view — "  a  contraction  or  an  augmentation  of  muscular  energy 
is  a  token  of  disintegration  ( =  dissimilation),  or  of  the  activity 
of  a  katabolic  or  motor  nerve,  so  is  relaxation  a  token  of  integra- 
tion ( =  assimilation),  i.e.  of  the  activity  of  an  anabolic  and 
inhibitory  nerve."  A  similar  view  was  previously  put  forth  by 
Lowit  (61)  in  connection  with  Hering's  theoretical  position. 
And  already  before  Gaskell's  work,  experiments  had  been  made 
(with  a  negative  result,  it  is  true)  to  determine  whether  the 
diastolic  vagus  -  arrest  of  the  heart  is  accompanied  by  any 
particular  galvanic  effects.  Wedenski  (62)  by  means  of  the 
telephone,  Taljantzeff  (63)  by  means  of  the  capillary  electro- 
meter, investigated  the  frog's  heart  during  vagus  arrest.  In 
the  first  case  there  was  no  sound,  in  the  second  case  the  meniscus 
did  not  move,  and  the  absence  of  any  kind  of  galvanic  action 
seemed  a  legitimate  conclusion.  With  excitation,  such  as  to 
produce  only  a  slowing  of  the  heart's  beat,  and  not  a  complete 
arrest,  Wedenski  heard  a  series  of  short  sounds  coinciding 
with  the  cardiac  rhythm,  and  corresponding  in  pitch  with  the 
inductorium.  But  to  attribute  these  to  the  action  of  motor 
fibres  of  the  vagus  is  a  very  questionable  proceeding.  One  thing 
is  clear  enough — it  is  hardly  practicable  to  devise  a  convincing 
experiment  upon  the  possible  galvanic  effects  of  vagus  excitation, 
while  the  normal  rhythmic  action  of  the  heart  persists ;  on  the 
other  hand,  it  is  no  easy  matter  to  obtain  a  prolonged  arrest  of 
the  heart  without  considerable  interference  with  its  anatomical 
and  functional  connections.  ISTevertheless  Gaskell  has  succeeded 
upon  the  tortoise  heart  in  obtaining  a  preparation  that  corre- 
sponds with  an  ordinary  nerve-muscle  preparation  in  that  the 
muscle  is  at  rest — the  nerve,  on  the  other  hand,  being  an  in- 
Mlitory  nerve.  In  the  tortoise  and  the  crocodile  a  particular 
nerve  (the  "  coronary  nerve ")  runs  alongside  of  one  of  the 
coronary  veins,  from  the  sinus  venosus  to  the  aortic  bifurcation. 

2  F 


434  ELECTRO-PHYSIOLOGY 


This  nerve,  together  with  the  sinus,  can  be  completely  isolated 
from  the  remainder  of  the  heart,  when  it  forms  the  sole  channel 
of  communication  to  the  auricle  which,  with  the  ventricle,  is 
separated  from  the  sinus.  After  the  separation  has  been  made, 
both  auricle  and  ventricle  remain  completely  quiescent,  and  only 
resume  pulsation  later,  so  that  the  experiments  can  be  effected 
during  the  quiescent  period.  To  this  end  the  apex  of  the 
auricle  is  burned,  yielding  in  consequence  a  strong  de- 
marcation current,  when  the  leading-off  electrodes  are  in  contact 
with  the  thermic  section  and  the  uninjured  base.  Like  the 
ventricle  current,  this  auricle  current  declines  rapidly  at  first, 
then  more  slowly.  During  this  time  each  vagus  excitation  gives 
rise  to  a  loositive  variation,  which  begins  quickly,  reaches  a 
maximum  in  about  10  sees.,  and  at  cessation  of  excitation 
sinks  with  increasing  rapidity,  so  that  after  18  —  20  sees,  the 
magnet  takes  up  the  position  which  it  would  have  occupied  in 
the  absence  of  vagus  excitation.  There  can  be  no  doubt  that 
this  effect  depends  upon  changes  that  have  arisen  in  the  un- 
injured part  of  the  auricle,  and  are  "  accompanied  by  increased 
positivity  of  that  part,  just  as  contraction  of  the  auricle  is 
accompanied  by  diminished  positivity  of  uninjured  tissue."  If 
the  auricle  now  recommences  to  beat,  each  contraction  gives 
rise  to  a  negative  variation  of  the  demarcation  current,  far  larger, 
as  a  rule,  than  the  positive  variation ;  cases,  however,  occur 
in  which  both  kinds  of  variation  are  about  equal  in  magnitude — 
yet  even  here  there  is  a  very  characteristic  difference  with  regard 
to  rapidity  of  decline  in  the  two  effects.  The  swing  back  of  the 
magnet  is  far  more  rapid  after  a  negative  than  after  a  positive 
variation.  If  the  excitation  of  the  vagus  is  continued  for  any 
length  of  time,  the  positive  variation  may  subside  completely, 
even  during  the  excitation.  These  galvanic  effects  of  the  vagus, 
like  its  inhibitory  function,  are  abolished  by  atropin  poisoning. 

As  is  well  known,  the  heart  is  influenced  not  only  by  in- 
hibitory, but  also  by  antagonistic,  viz.  excitatory,  nerve-fibres, 
which  suggests  the  possibility  of  obtaining  opposite  galvanic 
effects  by  excitation  of  the  latter.  And  Gaskell,  in  fact,  has 
succeeded  under  given  conditions  in  obtaining  a  negative  varia- 
tion of  the  quiescent  ventricle  (64). 

We  ourselves  performed  experiments  on  the  innervation  of 
the  claw-muscles  of  the  crab  (65),  the  results  of  which  will  have 


IV  ELECTROMOTIVE  ACTIOX  IN  MUSCLE  435 

to  be  discussed  more  fully  later  on,  bvit  which  showed  that  in 
this  case  also,  each  of  the  two  antagonistic  muscles  is,  like  the 
heart,  subject  to  the  influence  of  two  functionally  different  kinds 
of  fibres  (inhibitory  and  excitatory),  which  run  in  the  same  nerve- 
trunk,  and  are  capable  of  eliciting  opposite  mechanical  effects. 
It  was  natural  to  suppose  that  opposite  electromotive  effects, 
in  correspondence  with  this  antagonism,  would  obtain  in  the 
form  of  negative,  or  positive,  variations  of  the  muscle  current. 
But  there  were  considerable  difficulties  in  the  way  of  experi- 
mental investigation ;  in  the  cray-fish,  at  any  rate,  it  is  not 
possible  to  isolate  the  nerve  in  a  state  of  excitability,  while  the 
muscle  must  be  left  within  the  shell ;  this,  if  for  no  other  reason, 
is  imperative  from  the  mode  of  origin  of  the  component  fibres, 
which  spring  from  a  large  portion  of  the  inner  surface  of  the  last 
segment  of  the  claw,  and  for  the  most  part  converge  to  the 
tendon.  The  disposition  is  thus  very  similar  to  that  of  the 
tendinous  expansion  of  the  frog's  gastrocnemius.  At  whatever 
part  of  the  base  of  the  claw  the  shell  is  opened,  an  artificial 
transverse  section  of  the  muscle  is  inevitable,  and  it  is  nowhere 
possible  to  expose  the  uninjured  surface  (natural  longitudinal 
surface)  alone.  Under  these  circumstances  the  most  advisable 
proceeding  is  to  lead  off  from  an  injured  part  within  that  area 
of  the  claw  at  which  fibres  of  the  adductor  muscle  take  oriein 
(the  particular  position  of  this  led-off  point  is  in  general  of  no 
consequence),  using  as  a  second  lead-off  from  the  uninjured 
muscle  some  portion  of  the  electrically  indifferent  tissue  that 
occupies  the  interior  of  the  hollow  limbs  of  the  claw,  and  may 
to  some  extent  be  regarded  as  a  prolongation  of  the  tendon.  To 
this  end  a  small  piece  of  the  shell,  preferably  near  the  base  of 
the  claw,  is  broken  off  from  the  outer  edge,  towards  either  the 
outer  or  inner  surface,  by  bone-forceps.  A  second  smaller  opening 
is  made  at  about  the  middle  of  the  outer  edge  of  the  fixed  limb 
of  the  claw — the  small  adductor  muscle  having  previously  been 
completely  removed — to  serve  as  the  second  lead-off  of  the 
demarcation  current,  while  the  free  limb  of  the  claw  serves  to 
indicate  any  movement  due  to  altered  action  of  the  adductor. 
The  exciting  electrodes  (platinum  points)  transfixed  the  longest 
segment  of  the  claw  extremity  near  its  outer  border.  With  this 
disposition  the  lead-off  nearer  to  the  base  of  the  claw  is  of  course 
negative  to  the  distal  lead-off. 


436  ELECTRO-PHYSIOLOGY 


If  the  claw-nerve  is  now  tetanised  (the  demarcation  current 
having  been  previously  compensated),  the  usual  effect  with  the 
gradual  approximation  of  secondary  to  primary  coil  is  a  more 
or  less  considerable  deflection  in  the  direction  of  a  positive 
variation  of  the  demarcation  current,  followed  by  a  diphasic 
(negative  followed  by  positive),  and  finally  by  a  simple  negative 
deflection.  As  a  rule  the  positive  deflections  are  smaller  than 
the  negative  deflections.  With  regard  to  the  time-relations  of 
the  positive  variation,  it  may  be  remarked  that  the  variation, 
as  a  rule,  follows  close  upon  the  commencement  of  excitation, 
and  very  gradually  diminishes  during  its  course.  Owing  to  the 
fact  that  the  adductor  muscle  is  frequently  in  a  more  or  less 
pronounced  state  of  tonic  contraction  (which,  as  will  be  shown 
later,  may  be  abolished  by  weak  excitation  of  the  nerve,  whereas 
strong  excitation  always  augments,  or  initiates  contraction),  it 
seems  natural  to  bring  the  galvanic  changes  into  direct  causal 
relation  with  the  simultaneous  alterations  of  form  in  the 
muscle.  No  such  parallelism  of  the  two  orders  of  excitation 
effects  can,  however,  be  predicted.  It  frequently  appears  that 
the  electrical  effect  is  still  purely  positive,  or  diphasic,  while 
the  muscle  is  already  in  tetanus.  Nor  is  it  rare  to  find 
cases  in  which  the  adductor  muscle  contracts  vigorously 
with  a  certain  strength  of  excitation,  while  the  electrical 
changes  are  quite  insignificant,  there  being  either  a  visible 
antagonism  of  effects,  or  no  perceptible  result,  positive  or 
negative.  In  such  cases,  strong  currents,  as  a  rule,  produce 
negative  deflections  in  one  direction  only,  usually  insignificant 
in  magnitude,  and  followed  by  a  strong  positive  after-effect  when 
the  excitation  is  over.  Minimal  galvanic  effects,  or  complete  failure 
of  action,  frequently  occur  in  animals  which  have  been  exposed 
for  some  time  to  a  very  low  temperature  (0—5°  C.)  In  other 
cases,  under  the  same  conditions,  the  positive  variation  is  well 
marked  and  vigorous.  On  the  whole,  the  experimental  results 
obtained  vary  to  a  surprising  extent  in  different,  though  apparently 
similar,  crabs.  In  single  cases  it  was  found  possible  to  obtain 
positive  effects  in  one  direction  only,  with  any  given  strength  of 
excitation  after  very  strong  doses  of  curare,  although  the  muscle 
goes  into  tetanus  after  each  stronger  excitation,  so  that  there  is 
no  question  of  complete  curare  effect.  After  poisoning  with 
curare   the   positive  variation   is   always    strongly   developed   in 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  437 

comparison  with  normal  preparations,  even  if  deflections  in  the 
direction  of  the  negative  variation  occur  on  increasing  the 
stimulus.  Eventually  we  obtained  pure  positive  effects  in  one 
direction  by  the  application  of  a  simple  device,  viz.  fatiguing 
the  adductor  muscle  by  unilateral  exertion,  until  the  reactions 
from  the  motor  nerves  of  the  claw  were  reduced  to  a 
minimum. 

In  fresh,  lively  crabs  it  is  easy  to  fatigue  the  adductor  muscle 
in  a  comparatively  short  time  to  such  a  degree  that  voluntary 
or  reflex  contractions  are  only  possible  to  a  very  limited  extent. 
It  is  only  necessary  to  excite  the  muscle  into  vigorous  con- 
tractions, repeated  as  often  as  possible,  by  means  of  continuous 
stimulation  of  the  animal  (insertion  of  a  firm  body  and  finger 
between  the  joints  of  the  claws).  The  extraordinary  strength 
and  duration  of  the  first  contractions  diminish  with  surprising 
rapidity ;  longer  and  longer  pauses  are  required  before  the  crab 
can  be  stimulated  to  renewed,  effective  contraction  of  the  claws, 
and  finally  even  painful  excitation  ceases  to  produce  it. 

If  a  preparation  thus  fatigued  is  tested  as  above  in  regard  to 
its  electromotive  activity  during  excitation,  it  will  be  found 
without  exception  that  every  trace  of  a  negative  variation  is 
wanting,  while  strong  positive  dejlections  accomjjany  each  effective 
tetanisation  of  the  nerve.  The  effect  begins  in  different  animals 
within  a  tolerably  wide  range  of  current,  increases  to  a  certain 
limit  with  approximation  of  the  secondary  and  primary  coil,  to 
decrease  again,  as  a  rule,  with  further  increase  of  stimulus ;  this 
effect  may  perhaps  be  referred  in  part  to  an  interference  of  the 
two  opposed  effects  of  excitation,  as  is  indicated  inter  alia  by 
the  fact  that  at  a  lower  degree  of  exhaustion  of  the  adductor 
muscle  every  possible  transition  occurs  between  diphasic  action 
with  a  predominance  of  positive  deflection,  decreasing  in  size 
with  increasing  strength  of  current,  and  simple  positive 
variation. 

The  independence  of  the  galvanic  effects  of  excitation 
from  any  simultaneous  change  of  form  in  the  muscle,  is  quite 
unmistakable  in  these  experiments.  In  many  cases  mechanical 
effects  still  appear  in  a  fatigued  preparation  when  it  is  strongly 
excited  from  the  nerve,  and  are  expressed  in  a  shortening  of 
the  adductor  muscle,  which,  however,  is  then  accompanied,  not 
by  a   negative,    but   invariably  by    a   positive    variation    of  the 


438  ELECTRO-PHYSIOLOGY 


muscle  current.  In  other  cases  again,  all  change  of  form  is 
wanting  in  the  muscle,  even  with  the  strongest  excitation,  while, 
on  the  other  hand,  the  positive  variation  comes  out  in  apparently 
undiminished  proportions.  We  observed  the  same  phenomenon 
in  the  adductor  muscle  of  a  crab,  in  which  all  the  muscles  had 
undergone  pathological  change,  and  looked  gray,  as  if  from 
boiling.  These  experiments  show  definitely  that  a  positive 
variation  of  the  muscle  current  may  appear  in  consequence  of 
nerve  excitation,  not  merely  when  the  muscle  in  tonic  contraction 
relaxes,  but  also  when  it  is  free  from  tonus  and  exhibits  no 
change  of  form  on  excitation,  or  even  shortens  slightly.  With 
regard  to  the  time-relations  of  the  positive  variation,  it  must  be 
observed  that  the  beginning  of  the  deflection  coincides,  as  a  rule, 
with  the  beginning  of  excitation,  so  that  in  prolonged  tetanus  of 
the  nerve  the  scale  remains  some  time  at  maximal  deflection ; 
when  the  circuit  is  broken  it  returns  to  its  position  of  rest 
with  declining  rapidity,  but  fails  (in  the  initial  excitations)  to 
reach  it  completely,  so  that  the  muscle  current  at  first  increases 
steadily  in  consequence  of  nerve  excitation. 

If  a  preparation  which  is  in  such  a  state  that  every  effective 
excitation  produces  only  a  positive  variation  of  the  muscle  current, 
is  kept  for  a  long  time  at  a  low  temperature,  and  the  effect  of 
exciting  the  nerve  is  periodically  tested,  it  is  found  that 
the  deflections  under  similar  conditions,  with  uniform  strength 
of  coil  and  duration  of  closure,  are  gradually  lessened,  and  even 
change  their  sign  under  certain  conditions, — since  with  strong 
excitation  a  weak  negative  variation  appears  again,  either  as  the 
prelude  to  a  stronger  positive  variation,  or  independently.  Thus, 
after  a  long  rest,  a  fatigued  muscle  preparation  may  return  more 
or  less  to  the  normal,  characterised  by  diphasic  galvanic  effects 
of  excitation.  The  changes  referred  to  are  independent  of  the 
simultaneous  diminution  of  the  muscle  current,  which  may  easily 
be  excluded  by  further  supplementary  injury  to  the  parts  of 
the  muscle  still  uninjured.  If,  as  has  just  been  stated,  it  is 
possible  to  throw  the  adductor  muscle  of  the  crab's  claw  by 
prolonged  and  exhaustive  activity  from  the,  central  organ  on  the 
one  hand,  and  on  the  other  (though  less  certainly)  by  poisoning 
with  curare,  into  a  state  in  which  tetanisation  of  the  corresponding 
nerve  produces  only  a  positive  variation  of  the  muscle  current, 
it  is  still  easier  to   exclude  this  last   effect   entirely,  and,  under 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  439 

uniform  conditions  of  experiment,  to  produce  a  negative  variation  in 
only  one  direction.  This  is  readily  understood  when  we  remember 
that  the  negative  effects  preponderate  greatly  under  normal 
conditions,  while  the  opposite  positive  variation  appears  properly 
at  a  very  limited  range  of  the  scale  of  excitation,  while 
later  on  it  is  masked  completely.  In  order  to  abolish  it 
altogether,  it  is  only  necessary,  as  a  rule,  with  even  weak 
excitation,  to  keep  the  animals  under  experiment  for  several 
hours  in  water  at  20  —  25°  C,  or  to  leave  the  claws,  cut  off, 
for  some  time  (about  an  hour)  in  a  moist  chamber  at  normal 
temperature.  The  adductor  muscle  then  exhibits  an  electro- 
motive reaction  to  excitation  from  the  nerve,  which  is  the  exact 
opposite  to  that  of  continuous  activity.  While  the  muscle  thus 
exhibits  a  negative  variation  in  one  direction  only,  both  with 
the  minimal  excitation  from  the  nerve,  and  with  maximal 
currents  {i.e.  responds,  like  all  other  known  voluntary,  striated, 
vertebrate  muscles),  the  same  muscle,  under  uniform  conditions 
of  excitation  and  leading -off,  will  sometimes  yield  precisely 
opposite  electrical  changes,  expressed  in  a  positive  variation  of 
the  demarcation  current, — which  have  so  far  found  an  analogue 
only  in  vertebrate  cardiac  muscle.  These  two  opposite  variations  of 
the  muscle  current  exhibit  certain  striking  peculiarities,  as  regards 
both  strength  and  time-relations,  when  they  appear  as  the  sole 
effect  of  excitation  under  the  above  conditions ;  and  these  are 
not  without  importance  in  the  interpretation  of  the  phenomena. 
In  the  first  place,  it  is  found  that  in  the  one  case,  as  in  the  other, 
the  magnitude  of  the  deflections  on  the  galvanometer  is  nearly 
always  greater,  at  uniform  conditions,  than  it  is  in  a  perfectly 
fresh  normal  muscle  of  a  "  cold  crab."  In  such  a  preparation 
the  effect  in  one  or  the  other  direction  is  seldom  more  than 
50  degrees  of  the  scale,  while  in  a  fatigued  adductor  muscle  the 
positive  deflections  frequently  amount  to  100  divisions  of 
the  scale,  and  the  negative  effects  in  preparations  of  "  warm 
crabs  "  are  still  more  striking. 

In  the  normal  adductor  muscle  again  a  prominent  fact  is  the 
rapid  swing  back  of  the  negatively  deflected  magnet,  on  the 
prolongation  of  strong  excitation,  although,  as  is  easily  proved, 
the  tetanisation  of  the  muscle  persists  much  longer.  Not  in- 
frequently the  scale  flies  beyond  its  zero,  and  remains  deflected 
in  the  sense  of  an  opposite  positive  variation.      A  preparation  that 


440  ELECTRO-PHYSIOLOGY 


has  been  previously  heated  gives  quite  a  different  reaction ;  the 
negative  variation  in  this  case  quickly  reaches  its  maximum,  and 
only  diminishes  slightly  if  the  excitation  of  the  nerve  continues. 
The  magnet  only  returns  to  rest  when  the  circuit  is  broken. 
The  effect  is  therefore  similar  to  that  in  striated  vertebrate 
muscle.  We  have  stated  above  that  the  positive  variation  of 
the  fatigued  muscle  tends  at  first  to  a  permanent  increase  of 
the  demarcation  current,  while  later  on,  with  repeated  excitation, 
it  compensates  itself  each  time  slowly,  but  completely.  A 
negative  after-variation,  such  as  is  often  observed  on  strongly 
curarised  preparations,  is  regularly  absent  in  fatigued  muscle. 

The  next  question  connected  with  the  appearance  of  the 
positive  variation  on  indirect  tetanisation  of  the  adductor  muscle  is 
whether  there  is  here  a  discontinuous  alteration  of  state  in 
the  muscle -substance,  as  in  the  negative  variation  which 
otherwise  accompanies  excitation.  We  have  unfortunately  not 
been  able  to  decide  this  point  from  frog's  nerve -muscle  pre- 
parations, since,  under  even  the  most  favourable  conditions,  it 
seems  impossible  to  elicit  secondary  twitch,  or  secondary  tetanus, 
from  the  adductor  muscle.  Investigation  of  these  effects  by 
means  of  the  capillary  electrometer,  which  we  have  not  yet  been 
able  to  carry  out,  might  here  also  give  the  desired  solution.  In 
the  light  of  other  observations  on  the  same  preparation — to  be 
discussed  below — the  experimental  results  point  to  an  explana- 
tion, which  is  directly  connected  with  Gaskell's  theory,  as  above 
quoted.  Eemembering  that  the  adductor  muscle  of  the  crab's 
claw  is  supplied,  demonstrably,  by  two  functionally  distinct  nerves, 
inhibitory  and  excitatory  (assimilatory,  dissimilatory),  which  on 
excitation  produce  opposite  changes  of  state  in  the  muscle-sub- 
stance (expressed  by  antagonistic  changes  of  form  on  the  one 
hand,  and  by  contrary  electromotive  action  on  the  other),  it 
must  be  assumed  that  the  galvanic  effect  observed  with  a  moder- 
ate intensity  of  the  artificial  stimulus  to  the  nerve  is,  as  a  rule, 
the  result  of  co-operation  between  two  contrary  and  simul- 
taneously excited  processes,  the  alternating  ratio  of  which  depends 
on  the  one  hand  on  the  strength  of  excitation,  on  the  other  on 
the  temporary  condition  of  the  muscle. 

The  strongest  argument  in  favour  of  a  masked  diphasic 
response — even  in  such  galvanic  effects  as,  with  strong  excitation 
of  the  normal  adductor  muscle,   yield    experimentally   negative 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  441 

deflections  in  one  direction  only — derives  from  the  remarkable 
variations  in  magnitude  exhibited  vmder  approximately  equal 
conditions.  This  affords  a  prima  facie  explanation  of  the  striking 
fact  that  the  galvanic  effects  of  excitation  are  often  insignificant, 
even  in  preparations  made  from  fresh,  vigorous  animals,  and  may 
fail  altogether  at  a  certain  medium  strength  of  current.  This 
must  indeed  follow  inevitably,  where  the  two  antagonistic  processes 
terminate  simultaneously  as  regards  the  electrical  changes  which 
they  effect  in  the  muscle.  Finally,  both  the  diphasic  action  and 
the  interference  phenomena  before  alluded  to  (positive  after  varia- 
tion and  oscillation  of  the  magnet  to  a  new  equilibrium)  conform 
with  the  above  theory.  If  we  are  to  explain  the  monophasic,  but 
antagonistic  effects,  of  minimal  and  maximal  excitation,  we  must 
assume  in  the  first  case  a  more  prompt  reaction  of  the  in- 
hibitory (assimilatory)  processes,  in  the  other  a  preponderance 
of  the  process  initiated  in  the  muscle  by  the  exciting  (dissimi- 
latory)  fibres. 

Moreover,  we  find  experimentally  that  no  artificial  excitation 
of  the  nerve  produces  that  state  of  fatigue  in  the  muscle  in  which 
it  is  characterised  by  a  special  disposition  to  positive  galvanic 
effects,  while  these  never  fail  to  appear  when  fatigue  is  induced 
by  natural  excitation  of  the  nerve  from  the  central  organ.  This 
difference  is  intelligible  on  the  assumption  that  in  the  last  case 
the  exciting  fibres  are  alone,  or  mainly,  involved,  while  in  arti- 
ficial excitation  both  kinds  of  fibres  are  necessarily  excited 
simultaneously,  so  that  the  resulting  changes  of  the  muscle  in 
either  case  must  be  dissimilar. 

And  lastly,  we  must  emphasise  the  fact  that  in  indirect 
excitation  of  the  adductor  muscle  the  galvanic  effects  are  by  no 
means  in  such  close  relation  with  the  mechanical  effects  of 
excitation  as  might  be  concluded  from  countless  experiments  on 
vertebrate  nerve -muscle  preparations.  Eather,  as  has  been 
shown,  there  is  a  fundamental  independence  of  the  two,  since  not- 
withstanding the  marked  contraction  of  the  muscle,  the  galvanic 
effects  of  excitation  are  but  slightly  developed  under  some  con- 
ditions— although  in  the  right  direction  (negative  variation) — 
while  at  other  times  they  fail  altogether,  or  appear  as  a  positive 
variation.  From  this  we  must  conclude,  in  view  of  the  preced- 
ing observations,  that  the  antagonistic  relation  of  the  tioo  i^rocesses 
simultaneously  excited  in  the  muscle   may  hea,r  a   different   value 


442  ELECTRO-PHYSIOLOGY  chap. 

with  respect  to  the  mechanical  effects  of  excitation  and  to  the  electro- 
motive reaction ;  since  here  the  consequences  of  excitation,  and 
there  of  the  simultaneous  inhibition,  preponderate,  or  are  alone 
manifested. 

"We  must  further  point  out  the  analogy  between  this  reaction 
of  the  adductor  muscle  and  the  observations  of  Fano  on  the 
cardiac  muscle  of  the  tortoise,  where,  also,  there  is  imperfect 
correspondence  between  the  changes  of  form  in  the  muscle  and 
its  simultaneous  electrical  manifestations  (66). 

IV. — Secondary  Electromotive  Action  in  Muscle 

'j\        «  In  muscle  (as  in  nerve,  electrical  organs,  and  irritable  raiDto- 
^y         A^'plaain  in  general)  the  passage  of  the  electrical  current  is  Miowed 
\r        by  certain  electromotive  reactions,  which   are  intimatejy  related 
J*    ,  ^   with  me  action  current,  and  are  to  a  certain  extent  oifly  a  special 
flC/*^      form  oNits  manifestation.      As  early  as   1834,  Peltfer  discovered 
1*  that  fro^  limbs,  or  isolated  muscles,  or  even  nreces  of  muscle, 

developed  \  current  in  the  reversed  direction.   / 
qK  Du  Bois^teymond  (67),  who  took  up  th^investigation  later, 

)^  convinced  hin^elf  that  the  secondary  c^^nt  (after-current)  is 

T,«       not  exclusively^  at  all,  dependent  o^the  polar  zones,  but  is 
JC'  also  initiated  in  tS^  tracts  lying  bal^een  them,  since  he  found 

that  any  given  seodon  of  the  Mtrapolar  tract  of  a  muscle 
traversed  longitudinalW  gave  aiyelectromotive  response  in  the 
same  direction,  on  opening  tho^polarising  current ;  accordingly 
he  advanced  the  view  thM  ^i^s  effect  mainly  depended  on  so- 
called  "  internal  folarisatiov^ 

Many  inorganic  and  c^aiilc  porous  bodies,  saturated  with  an 
electrolyser,  do  actuall;^possess  ri^  property  of  acquiring  negative 
internal  polarisation.  /The  polaris'j^g  current  then  divides  itself 
between  the  badlwTonducting,  satuiwng  fluid,  and  the  porous 
vessel,  the  lattei^eing  polarised  froni\the  zones.  "Each  of 
the  countless  intermediate  points  now  g^es  an  electromotive 
reaction  inylfne  reverse  direction  from  thatSin  which  it  was 
traversed^fy  the  current."  The  superposition  onall  these  partial 
current^esults  in  the  branch  current,  which  passes^  through  the 
deriv^fng  circuit.  Each  coextensive  tract  in  any  sucK  regularly 
CMKtructed  prismatic,  or  cylindrical,  body  gives,  as  a  rule/^  strong 
afecondary  electromotive  reaction  after  the  passage  of  the  current. 


V 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  443 

It\was  soon  observed  that  living  muscle,  traversed  by  current, 
behaves  in  this  respect  very  differently  from  dead  organic^  or 
inorganic,  bodies,  more  especially  in  that  positive,  as  \yell  as 
negativ^^  after-currents  appear  under  some  conditions,  ^or  the 
investiga!W)n  of  polarisation  effects  in  muscle,  du  Bois-Reymond 
generally  Vsed  the  gracilis  and  semimembranosus^  muscles, 
stretched  cmaveniently.  A  pair  of  non-polarisabl/  electrodes 
on  each  side  s^ved  to  lead  in  the  polarising  current!;  and  to  lead 
oft'  the  polarisauyon  current.  The  second  pair  were/usually  placed 
between  the  others,  within  the  intrapolar  area.  /A  special  con- 
trivance made  it  possible  to  alter  the  "  period/of  closure  " — i.e. 
the  time  during  waich  the  polarising  current/ was  sent  through 
the  object  to  be  polarised — from  O'OOl  to  ^0  sees.  The  same 
contrivance  effected  Vlosure  of  the  galvai/ometer  circuit  after 
breaking  the  batterA  circuit  at  a  imnimal  and  constant 
interval.  \  / 

The  secondary  elec^pmotive  effec^  observed  under  these 
conditions  of  experiment  m  the  musdre  are  essentially  dependent 
on  the  density  and  duratioX  of  the/primary  current,  while  they 
are  much  confused  from  th\  pemstent  interference  of  negative 
aiid  positive  action.  "  With  V/current  density  lower  than  that 
of  two  Groves,  and  with  quite  sAhort  closure,  no  polarisation  is,  as 
a  rule,  perceptible  in  the  g^QvaVometer.  The  first  traces  found 
with  one  Daniell  and  1  sec.  cloteure  are  negative.  The  first 
positive  traces,  on  the  otner  hand,  >first  appear  with  two  Groves, 
and  about  0"3  sec.  closirjre."  \ 

With  an  increasing  period  of  closu^^;  ^^^  Bois-Eeymond  found 
that  the  positive,  polarisation  quickly  reached  its  maximum,  to 
decrease  more  slowl/,  and  pass  over  into  negative  polarisation,  which 
on  its  side  agair/  rises  to  a  maximum.  >He  fixes  the  "  critical 
point "  of  closii^  as  that  at  which  positiv^nasses  into  negative 
polarisation.  /The  strongest  positive  polarisatW  in  these  experi- 
ments was  a/ a  closure  of  0-0075  sees,  with  2^0  Groves  (!),  the 
strongest  iregative  polarisation  at  1 0  minutes'  clo^lre  of  1  Grove. 
Short  impacts  of  current  (induction  shocks)  producXonly  positive 
polarissrtion.  \ 

Both  positive  and  negative  polarisation  are  very  j^ersistent, 
and/sometimes  outlast  the  opening  of  the  polarising  curtent  for 
2/ minutes  or  more.  If  they  are  initiated  at  the  critical\oint, 
ofu  Bois-Eeymond  not  infrequently  observed  a  diphasic  variaHpn, 


444  ELECTRO-PHYSIOLOGY  chap. 

NMrresponding  usually  with  first  a  negative  and  then  a  positive 
polarisation.  This  is  due  to  the  fact  that  from  the  mon?fent 
of  Mosure  onwards,  loth  kinds  of  polarisation  are  simultaneously 
present,  but  increase  in  different  proportions,  "  negative  Polarisa- 
tion infereasinfj  more  in  ratio  with  the  time  of  closure,/vhile  the 
positive  Variation  is  augmented  quickly  at  first  andAhen  more 
slowly."  \  / 

Du  Bods-Eeymond  further  concluded  from  /xperiments  in 
which  the  W)per  and  lower  half  of  regular  nujRcles  were  alter- 
nately traA^erslsd  by  the  current,  and  tested  foi/ polarisation,  that 
"  strong  positiv\  polarisation  is  exhibited  in  tVie  upper  half  in  an 
ascending,  in  th\  lower  half  in  a  descendiiig,  direction."  Dead 
muscles  still  exhibit  traces  of  negative  /nternal  polarisability 
which  is  completelyNabolished  only  by  bdling ;  positive  polarisa- 
tion, on  the  other  Imnd,  is  exclusively  characteristic  of  living 
muscle.  Du  Bois-Ee;miond  conclude/  that  "  it  is  not  electro- 
motive forces,  homodronmiis  with  th^primary  current,  which  are 
generated  by  the  positive^'  polarisa^^le  tissues,  but  the  carriers 
of  electromotive  forces  already  pngsent  (electromotive  molecules) 
which  are  homodromously  adVst/d  with  the  primary  current." 

How  little  these  results  raally  go  to  support  the  molecular 
theory,  however,  is  strikinglyyob^dOus  in  the"  later  investigations 
of  Hering  and  Hermann  (6/— 69)S.  Hering  proves  conclusively 
that  there  can  be  no  que/tion  of  Maternal  positive  or  negative 
polarisation  in  a  longitminally  trav^-sed  muscle  in  du  Bois- 
Eeymond's  sense,  sincer  the  actual  seat  of  the  electromotive 
changes  induced  by  tlae  exciting  currentVlies  at  those  points  of 
the  contractile  substjmce  by  which  the  cu^ent  enters  or  leaves 
the  muscle  (the  physiological  pole),  so  th^  the  close  relation 
between  these  menomena  and  the  polar  erfects  of  current  is 
unmistakable.    /  \ 

If,  in  the/same  sense  as  above,  we  regard  every  change  in  the 
chemical  actifvity  of  any  part  of  the  muscle-fibre  )|^  the  sine  qua 
non  of  thor  appearance  of  electromotive  action,  weVshall  premise 
that  on/lending  current  through  a  muscle  with  parallel  fibres, 
the  chemical  alteration  of  the  contractile  substanc\  recurring 
presumably  at  the  physiological  kathode  and  anode  wirl  initiate 
diffidences  of  potential,  which  must  be  discovered  when  >^e  or 
dmer  end  so  altered  of  the  muscle  is  led  off  in  conuection\yith 
/  point   of  the  unaltered  surface   of  the   muscle.      The   resiiHs 


ELECTROMOTIVE  ACTION  IX  MUSCLE 


445 


obtained  by  Hering  from  such  experiments  on  the  frog's  sartorius 
aerially  correspond  throughout  with  this  assumption. 

the  muscle  is  fixed  at  moderate  tension,  and  current/sent 
throu^  it  from  the  stumps  of  bone  on  either  side,  on  lead^g  oft' 
from  01^  or  the  other  tendon-end,  and  from  a  point /on  the 
longitudiiM  surface,  the  muscle  current  measured  previous  to  ex- 
citation is  ^md  on  opening  the  circuit  to  be  consideraJ61y  altered, 
i.e.  increased,  (diminished,  neutralised,  or  reversed,  in  covrespondence 
with  the  direcmon,  strength,  and  duration  of  the  exciting  circuit, 
and  the  strengtlXand  direction  of  the  original  musifle  current.  If 
the  muscle  curreirt  has  previously  been  compensated,  positive  or 
negative  increase  of  the  "  polarisation  currents/ — corresponding 
with  the  muscle  cu»rent — will  appear,  and  /nay  be  positive  or 
negative,  i.e.  parallel  ^wth  the  exciting  currem,  or  opposed  to  it  in 
direction.  Since  theseXhave  their  real  origin  in  the  anodic  and 
kathodic  points  of  the  Vnuscle  -  substancie,  Hering  distinguishes 
between  anodic  and  JcatJwdic  polarisati«<ii.  The  former  may  be 
either  positive  or  negative,  aiccording  t/the  strength  and  duration 
of  the  exciting  current,  theXlatter  Jni  the  majority  of  cases  is 
negative  only. 

With  a  short  closure,  verA^eak  currents  invariably  yield 
a  negative  polarisation  current  Al  fresh  muscle,  so  long  as  only 
the  anodic  tendon-end,  and  aypoiut  at  about  the  middle  of  the 
muscle  surface,  are  in  circui^  WitK  stronger  excitation  currents, 
on  the  other  hand,  and  noyxoo  brief  Vlosure,  ^j'ost^'ire  polarisation 
only  results,  which  increj^es  with  tha  strength  of  current,  and 
finally  far  surpasses  th^trongest  negatiVe  anodic  polarisation. 

Very  strong  currents  produce  positiv^polarisation,  even  with 
minimal  closure,  whfle  weaker  currents,  wim  short  closure,  excite 
negative,  or  diphasic  (first  negative,  then  positive)  polarisation, 
and  produce  a  positive  effect  after  prolonged Vlosure  only.  In- 
duction current  also  cause  a  similar  reaction  t\  strong  constant 
currents,  wi^  minimal  closure,  since  they  only  p\|oduce  positive 
anodic  polarisation. 

All  ^ese  polarisation  effects  (after-currents)  are  \^holly  want- 
ing, oryappear  as  a  trace  only,  if  both  leading- off  elecb'odes  are 
appliofQ  to  the  longitudinal  surface  of  the  muscle,  withoi^  being; 
tooyClose  to  one  or  the  other  end  of  it. 

Since,    according    to    Hermann's    alteration    theory,    exited 
iuscle-substance  is  negative  towards  unexcited  substance,  tn^e 


446 


ELECTRO-PHYSIOLOGY 


be  no  doubt  (in  view  of  the   conditions  and  behaviour  of 

break  excitation  in  muscle)  that  positive  anodic  polarisa- 
tioiA  is  an  expression  of  the  same,  i.e.  the  positive  pola^sation 
currmt  produced  hy  alterations  of  anodic  points  of  the^ontractile 
suhsta/S^e  is  an  action  current  due  to  the  break  exdaation  from 
the  armde ;  an  action  current  which  behaves  yj^j  differently 
from  thX  action  current  produced  by  the  mak^excitation  that 
has  so  far*^xclusively  concerned  us.  / 

The  loW  persistence  of  negativity  in  thre  anodic  points  is 
most  remarkable ;  it  is  easily  explained  by  the  fact  that  the 
opening  of  a  \onstant  current  under  Bome  conditions  leads  to 
protracted  excitation  (persistent  opening  contraction)  of  the 
muscle.  This  gmlually  declines,  beino^ore  and  more  confined 
to  the  anodic  point\  of  the  muscle.  B^t  even  when,  as  on  sending 
in  weaker  currents,  Vr  with  a  shortey  duration  of  strong  currents, 
there  is  no  visible  persistent  break  contraction,  or  even  break 
twitch,  there  is  nothingyto  preven^  us  from  regarding  the  positive 
polarisation  current  in NguestiouT  as  the  expression  of  opening 
excitation  lasting  for  a  coasideryLle  period, — since  a  low  degree  of 
contraction  is  difficult  or  iom&ssible  of  demonstration,  especially 
when  it  is  confined  to  the  immediate  vicinity  of  the  anodic  or 
kathodic  points  of  the  musdre,  and  since,  moreover,  negativity  may 
be  present  as  the  expression  of  \xcitation,  without  any  trace  of 
contraction.  /  \ 

Hermann's  view  oy  the  positivX  anodic  after-current  only 
differs  from  that  of  Alering  inasmVh  as,  starting  with  the 
assumption  of  an  inj^apolar  electrotonr^,  he  derives  the  action 
current  at  break  ^om  the  whole  anelWitrotonic  tract  of  the 
muscle.  We  ha^  already  seen,  on  theVontrary,  that  if  the 
currents  employed  are  not  too  strong,  all  theychanges  which  can 
collectively  beytermed  "  electrotonus  "  are  strimy  confined  to  the 
physiological /lectrode  points.  \ 

Kathod^  polarisation  is  almost  exclusively  negqiive  in  striated 
muscle.  Ji  first  appears  on  leading  off  in  the  sarrorius,  through 
^rent  is  passing,  from  the  kathodic  end  and  Centre  of  the 
with  very  weak  currents,  after  a  closure  W  several 
,  increasing  steadily  with  increase  of  current  and  longer 
If  it  is  compared  with  the  positive  anodic  after-o^rrent 
appears   at    the    same    end    of  the    muscle,    with  '^qual 


brength,  and  duration  of  closure,  the  latter  soon  becomes  by  far 


ELECTROMOTIVE  ACTION  IN  MUSCLE  447 

the  stronger.  With  very  strong  currents  and  long  closure, >aie 
nWative  kathodic  polarisation  may  become  as  strong  as^  the 
equ^^ly  abterminal  muscle  current  which  shows  itself — the 
electrodes  being  unaltered — on  killing  the  end  of  thor  muscle. 
Induction  currents,  too,  give  negative  kathodic  polaris^ion,  but  it 
is  essentiMly  weaker  than  the  positive  anodic  poltmsation  pro- 
duced by  me  same  strength  of  current  on  the/same  muscle 
(sartorius).  ^le  conclusion  therefore  is  that  with  arowing  strength 
and  duration  of  the  exciting  current,  the  katho/ic  region  of  the 
muscle  (physiological  kathode)  becomes  increasuftgly  more  negative 
in  comparison  \mh  the  centre.  If  this  mere  an  ec[uivalent 
phenomenon  to  thofee  of  physical,  internal  Polarisation,  the  nega- 
tive polarisation  curi^nt  would — as  has  b^n  shown — necessarily 
appear  in  approximate^  equal  proportioiys  on  leading  oft'  from  any 
point  of  the  interpolarVtract,  and  this,yas  Hering  shows,  never  is 
the  case.  When  the  wo  galvanonreter  electrodes  are  placed 
at  the  margin  between  theVipper  ancLoniddle  third  of  the  sartorius, 
the  exciting  current  being  i^d  in  as  before  through  the  bones,  no 
polarisation  current  can  be  oJpser^ed,  or  it  is  so  insignificant  as 
compared  with  the  anodic  ana  Icathodic  polarisation  that  it  may 
practically  be  neglected.  TheAelatively  weak  effects  in  the  inter- 
polar  tract  on  the  applicajtioiX  of  very  strong  currents,  with 
prolonged  closure,  are  suffipentl^  explained  by  the  fact  that  the 
polar  points  of  the  musdle  are  pever  limited  exclusively  to  its 
ends, — due  inter  alia  \Jb  the  factXthat  the  sartorius  not  infre- 
quently exhibits  short/fibres  whichXend,  or  begin,  somewhere  in 
the  length  of  the  nyfscle.  On  theVther  hand,  the  appearance 
of  persistent  openinig  and  closure  contraction  of  course  produces 
inequalities  in  tbre  individual  parts  \f  the  interpolar  region. 
There  is  thus  ii^  reason  for  assuming  iirternal  polarisation  of  the 
muscle -substance  in  du  Bois-Eeymond's  se^se.  All  the  jplunomena 
of  negative,  h/thodic  polarisoMon  can  he  referred  to  chemical  cdtera- 
tion  (excitaJion,  or  loccd  fatigue^  in  the  kathodic  points  of  the  fibres 
collectiveh 

No/  are  the  later  experiments  of  du  BoisSReymond  more 
conviurcing,  in  which  the  application  of  a  current%f  ten  Grove 
cells/to  the  curarised  sartorius,  produces  after  15— 2^minutes' 
cloafure  "  a  secondary  electromotive  force  in  the  reverse  oo-ection 
t(/ the  polarising  current  in  every  tract  of  the  muscle,"  its  m^gni- 
(ide  increasing  with  the  length  of  the  tract  led  off.      For  \he 


448 


ELECTRO-PHYSIOLOGY 


extent  to  which  the  excitability  and  conductivity  of  the  mjii^cle 
is\  altered  by  such  impossibly  strong  currents  is  suffi<Gently 
attested  by  the  appearance  of  the  galvanic  wave  unidfer  these 
conditions,  as  well  as  by  the  persistent  excitation  (often  excess- 
ively marked  and  widely  distributed  over  the  intim)olar  muscle 
tract),  m  the  region  of  the  anode,  which  depends^  as  was  shown 
above,  uV)n  the  effectuation  of  secondary  electr/de  points.  But 
there  caiA  hardly  be  a  question,'  after  the  foregoing  discussion, 
that  experiments  performed  under  such  abnormal  conditions  in 
no  way  coirfcravene  the  clear  and  simple/  result  of  Hering's 
investigations) 

The  most  striking  proof  that  secondary  electromotive  pheno- 
mena are  pure  \plar  effects  of  current  W',  however,  the  fact  that 
killing  the  anodi\  or  kathodic  points  of  the  muscle  hinders  the 
appearance  of  botN  positive  and  negative  kathodic  polarisation, 
exactly  as  occurs  ia  the  opening  am  closing  excitation.  The 
negative,  and  still  roore  the  positiire,  polarisation  current  thus 
implies  integrity  of  thOykathodic  oy  anodic  points  of  the  excitable 
substance. 

Hermann  pointed  th^  out /n  regard  to  the  positive  anodic 
after-current  in  muscle,  de\igna!xing  it  in  consequence  an  "  irrita- 
tive "  negative  after-current,\^.  that  "  derived  from  true  polarisa- 
tion." Like  du  Bois-Eeyn^rafad,  he  derives  the  latter  from  the 
whole  interpolar  tract,  arm,  affier  partial  passage  of  current,  from 
the  extra -polar  region /also,  ia  consequence  of  a  polarisation, 
which  he  takes  to  be  equivalent  with  certain  polarisation  pheno- 
mena (infra)  that  /ccur  in  meduUated  nerves,  and  can  be 
reproduced  upon  aypolarisable  wire  Neurrounded  by  an  electrolyte, 
through  the  sheatJi  of  which  the  current  enters.  He  finds  that 
the  effects  upon /his  ("  core  ")  model  cokicide  with  the  polarisation 
phenomena,  bpih  inter-  and  extra-polar,Vf  muscle  and  nerve,  the 
"  polarising  arter-current "  being  in  the  fin|t  place  heterodromous, 
in  the  secoml  place  homodromous,  with  theVolarising  current. 

We  shall  enter  more  fully  into  these  \elations  when  dis- 
cussing pie  electrical  excitation  of  nerve ;  foi\the  present  it  is 
enough'  to  say  that  just  as  these  effects  are  indisputable  under 
certaiii  conditions,  so  too  in  muscle,  within  a  giVen  "  physio- 
logical "  range  of  strength  of  current,  the  negative  kaM^odic  must, 
equally  with  the  positive  anodic,  be  designated  an  "  irritative " 
sffter- current,  due  entirely  to  polar  current  action.  \ 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  449 

The  earlier,  and  contrary  results  of  dii  Bois-Eeymond 
are,  as  Hering  showed,  to  be  referred  to  the  fact  that  he  em- 
ployed two  muscles,  one  of  which  was  entirely,  the  other  at  least 
partially  traversed  by  a  tendinous  intersection.  On  leading  off 
from  two  points  of  the  interpolar  tract,  there  must  as  a  rule  be 
countless  anodic  and  kathodic  points  between  the  contacts  of 
the  leading-off  circuit,  more  especially  when  the  tendinous  wall 
of  partition  (running  obliquely  to  the  muscle  axis,  and  dividing 
each  of  the  two  muscles  so  as  to  form  two  separate  muscles  lying 
one  behind  the  other)  falls  completely  within  the  two  galvano- 
meter ,  electrodes.  In  front  of  the  intersection  the  current 
leaves  by  the  fibres  of  one  of  these  separate  muscles,  to  enter 
again  by  the  fibres  of  the  second.  On  one  side  of  the  inter- 
section therefore  there  are  countless  kathodic,  on  the  other  as 
many  anodic,  points,  and  both  are  the  seat  of  polar  changes. 

Here  too  du  Bois-Eeymond  has  recently  tried  to  give  another 
interpretation  from  the  standpoint  of  the  molecular  theory,  but 
it  is  so  obviously  inadequate  that  he  himself  recognised  its  great 
difficulties,  which  are  not  removed  by  a  whole  series  of  accessory 
hypotheses.  The  polarisation  effects  in  the  gracilis  muscle  are 
derived  by  this  theory — tested  on  a  "  clay  dummy  "  (consisting 
of  a  round  clay  stamp,  hollowed  out  in  the  centre,  with  the 
patellar  tendon  of  a  frog  clamped  between  its  two  halves) — from 
"  an  axially  directed,  antagonistic  force,  initiated  in  each  super- 
ficial element  of  the  intersection."  Experimental  observations, 
however,  did  not  correspond  with  the  theoretical  response  of  the 
muscle,  and  du  Bois-Eeymond  was  compelled  to  adopt  the  theory 
of  a  "  false  internal  polarisation,"  for  which  no  explanation  is 
given.  The  parelectronomic  tract,  or  layer,  on  the  other  hand, 
is  the  seat  of  "  true  "  polarisation  at  the  ends  of  fibres.  Du  Bois- 
Eeymond,  however,  considered  it  impossible  to  refer  this  to  the 
negative  variation,  because  "  no  such  relation  seems  to  obtain 
between  the  mechanical  effects  of  excitation  and  polarisation,  as 
must  exist  if  polarisation  is  to  be  conceived  as  the  after-effect  of 
negative  variation,  or  as  the  negative  variation  proper."  He 
therefore  takes  no  account  of  the  fact  that  such  complete  parallel- 
ism exists  just  as  little  between  the  visible  effects  of  the  opening 
excitation  and  the  positive  anodic  after-current,  although  there 
can  be  no  doubt  as  to  the  causative  connection  between  them. 
Du  Bois  indeed   goes  so  far   as  to   deny  the   presence  of  per- 

2  G 


450  ELECTRO-PHYSIOLOGY  chap. 

sistent  excitation  in  the  sartorius,  on  the  strength  of  experiments 
similar  to  the  polarisation  experiments.  This  is  not  the  place 
to  enter  further  into  the  discussion,  which  may  be  referred  to 
Hering's  recent  criticism  (68). 

At  first  sight  an  argument  in  favour  of  du  Bois-Eeymond's 
view,  and  against  that  of  the  positive  anodic  after-current  as  the 
galvanic  expression  of  the  opening  excitation,  might  be  deduced 
from  the  fact  that  these  effects  of  the  passage  of  current  appear 
equally  when  the  muscle  is  in  deep  ether  narcosis,  a  condition 
in  which  the  strongest  excitation  fails  to  produce  any  trace 
of  visible  change  of  form.  Thus  it  would  seem  as  if  the  local 
capacity  of  reaction  in  the  muscle  were  not  perceptibly  affected 
by  narcosis  (as  far  as  may  be  judged  from  the  galvanometric 
changes  visible) ;  since  the  capacity  of  the  muscle  to  yield 
a  positive  anodic  after-current,  when  stimulated  by  the  electrical 
■current,  is  not  merely  unimpaired  by  protracted  treatment  with 
ether,  but  is  even  considerably  augmented — it  subsequently 
remains  constant  for  some  time,  and  only  diminishes  perceptibly 
at  a  much  later  period.  If  the  negative  kathodic  polarisation 
of  the  etherised  muscle  is  similarly  investigated,  it  is  also 
found  to  undergo  no  diminution  during  narcosis. 

In  both  cases,  however,  the  appearance  of  the  after-current 
is  affected  or  totally  hindered,  as  under  normal  conditions,  on 
killing  the  anodic  or  kathodic  ends  of  fibres.  In  place  of  the 
positive  anodic  polarisation,  a  much  weaker,  negative  after-effect 
may  then  be  observed,  while  no  trace  remains  of  the  negative 
kathodic  polarisation,  even  with  prolonged  closure. 

The  idea  of  excitation  is  so  closely  allied  in  the  muscle 
with  that  of  active  change  of  form,  or  at  least  the  possibility 
of  the  same,  that  the  hypothesis  of  a  prolongation  of  excita- 
bility when  contractility  has  been  entirely  abolished,  encounters 
a  priori  difficulties.  Secondary  electromotive  manifestations 
appear  indeed  in  a  rigidly  stretched  muscle,  but  then 
both  conductivity  and  the  negative  variation  are  still  present, 
and  the  muscle  would  contract  in  toto  if  not  mechanically 
hindered.  The  ether  muscle,  on  the  other  hand,  has  not  only 
completely  lost  its  power  of  shortening  on  excitation,  but  has 
also  become  wholly  incapable  of  conducting.  The  great  majority 
■of  experiments  in  muscle  and  nerve  physiology,  however,  justify 
us  in  assuming  a  close  relation  between  conductivity  and  excita- 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  451 

bility,  although  on  the  other  hand  the  changes  in  the  two 
functions  do  not  always  keep  pace,  and  the  one  faculty  may  be 
already  abolished  while  the  other  is  still  in  existence.  We  need 
only  in  this  connection  refer  to  the  fact  that  in  the  process  of 
dying,  the  manifestations  of  contraction  which  appear  with 
mechanical  or  electrical  excitation  become  more  and  more  con- 
fined to  the  seat  of  direct  stimulation,  where  they  are  still 
energetic  when  conductivity  has  been  entirely  arrested  ("  idio- 
muscular  contraction").  This  is  generally  explained  on  the 
assumption  that  the  conductivity  of  the  muscle  disappears,  with 
diminishing  excitability,  before  its  direct  capacity  for  response. 
The  same  thing  may  be  observed  in  the  course  of  ether  narcosis 
also,  since  electrical  excitation  in  the  region  of  the  kathode  still 
produces  a  plain  contraction ;  although  on  exciting  one  end  and 
leading  off  from  the  other  no  trace  remains  of  any  negative 
variation  of  the  demarcation  current,  i.e.  conductivity  is  almost 
entirely  abolished.  In  view  of  these  facts  it  is  natural  to  ask 
whether  the  continuation  of  polarisation  effects  might  not  be 
referred  to  exclusive  localising  of  both  opening  and  closing 
excitation  to  the  extreme  ends  of  the  muscle-fibres,  the  shorten- 
ing of  which  might  easily  escape  undetected.  No  such  effect, 
however,  is  indicated  by  microscopic  observation  of  the  muscle 
traversed  by  current,  and  it  may  be  assumed  that  with 
sufficiently  prolonged  etherisation  all  perceptible  trace  of  local 
contraction  disappears  (in  excitation  with  the  electrical  current), 
although  the  polarisation  effects  in  question  may  be  observed  in 
full  vigour  before  as  well  as  after.  We  may  conclude  therefore 
that  the  manifestation  of  the  changes  which  iinclerUe  the  after- 
current is  quite  independent  of  the  persistence  of  contractility 
and  conductivity. 

This  does  not,  however,  exclude  the  view  by  which  positive 
anodic,  and  negative  kathodic,  after -currents  are  regarded  as 
the  consequences  of  break  and  make  excitation,  but  may  be 
brought  into  agreement  with  it,  if  the  possibility  of  localised 
excitation  without  simultaneous  change  of  form  in  the  muscle 
is  admitted.  This  possibility  is  the  less  to  be  doubted  since 
the  same  phenomena  also  appear  under  perfectly  normal  con- 
ditions. We  need  only  refer  to  the  fact  that  with  direct 
electrical  excitation  of  the  muscle  there  will  *al ways  be  a  limit 
of    strength   of    stimulus    below   which    the    current   no   longer 


452  ELECTRO-PHYSIOLOGY  chap. 

discharges  perceptible  mechanical  excitation  effects,  although  it 
still  works  changes  in  the  muscle-substance  which  are  expressed 
in  other  ways,  more  especially  by  an  alteration  of  excitability 
at  the  points  of  entrance  and  exit.  Further,  it  is  known  (as 
Hering  pointed  out)  that  the  break  excitation  may  be  identified 
on  the  galvanometer  as  a  positive  anodic  after- current,  "  even 
where  this  is  not  visible  to  the  eye,  nor  even  perhaps  micro- 
scopically." At  all  events  there  are  excitations  which  must  be 
termed  subliminal  as  regards  change  of  form  in  the  muscle, 
while  in  a  narcotised  muscle  the  strongest  excitation  fails  to 
develop  any  directly  visible  reaction.  These  facts  make  it  clear 
that  the  relation  between  contraction  and  excitation  is  by  no 
means  so  immediate  as  might  a,  -priori  be  supposed,  but  that  the 
indirectly  demonstrable  changes  in  the  muscle -substance  may 
occur  in  consequence  of  previous  excitation,  without  perceptible 
changes  of  form.  And  it  is  very  remarkable  in  the  etherised 
muscle  that  the  polarisation  effects  described  show  no  perceptible 
weakening  throughout  the  entire  period  of  narcosis.  This  tells 
in  favour  of  the  fundamental  independence  of  excitability  in  the 
muscle  from  its  contractility  and  conductivity. 

Under  these  circumstances  it  is  the  more  interesting  that  the 
possibility  of  excitation  seems  to  exist  in  another  and  different 
alteration  of  the  muscle -substance,  in  which  contractility  is 
equally  more  or  less  affected.  In  this  case  it  is  not  merely 
the  polarisation  phenomena  under  discussion  that  continue, 
but  (where  the  changes  that  occur  are  local,  and  con- 
fined to  the  seat  of  direct  excitation)  there  are  also  changes 
of  form  in  the  normal  section  of  the  muscle.  We  have 
already  seen  that  striated  muscle  is  capable  of  taking  up  a 
considerable  bulk  of  water  without  losing  its  capacity  for  elec- 
tromotive response,  when  irritated,  as  under  normal  conditions. 
If  the  water  treatment  is  confined  to  one  or  the  other  end  of  a 
sartorius,  this  end  may  in  consequence  of  imbibition  undergo 
great  alteration  in  its  physical  properties,  without,  as  we  have 
seen  above,  becoming  negative  to  the  uninjured  part  of  the  pre- 
paration. This  agrees  with  the  fact  that  excitability  towards 
the  electrical  current  is  not  perceptibly  affected,  if  it  is  sent 
through  the  muscle  in  such  a  way  that  the  point  of  direct  ex- 
citation is  situated  at  the  altered  end  of  the  muscle.  This  is  found 
on   the   one  hand  from  comparing   the  height   of  twitch,  on  the 


IV  ELECTROMOTIVE  ACTIOX  IN  MUSCLE  453 

other  from  the  behaviour  of  secondary  electromotive  phenomena 
before  and  after  local  treatment  with  water.  The  mechanical, 
like  the  galvanic,  effects  of  excitation  are  invariably  altered  in 
the  same  way  (provided  the  point  of  direct  excitation  coincides 
with  the  injured  end  of  the  muscle)  by  every  kind  of  stimulus, 
localised  application  included,  which  produces  radical  injury  of 
the  chemical  properties  of  the  muscle-substance :  we  are  there- 
fore forced  into  the  conclusion  that  the  excitability  of  the 
swollen  section  of  the  fibre  does  not  at  first  suffer  perceptibly  in 
the  case  under  consideration.  On  the  other  hand,  there  is  no 
doubt  that  its  contractility  diminishes  considerably  in  con- 
sequence of  the  rigor-like  condition  of  the  muscle,  even  in  the 
earliest  stages  of  the  water  effect.  When,  notwithstanding,  not 
merely  the  continuance  of  the  positive  anodic,  and  negative 
kathodic  after -currents,  but  also  vigorous  make  and  break 
twitches,  are  observed  on  sending  current  in  or  out  at  the  end 
treated  with  water,  we  must  inevitably  conclude  that  capacity 
for  active  change  of  form  at  the  seat  of  direct  excitation  is 
not  essential  to  excitability  in  the  muscle.  It  follows  that  the 
complete  loss  of  contractility  in  the  etherised  muscle  can,  as 
little  as  that  of  conductivity,  be  regarded  (under  similar  con- 
ditions) as  a  valid  objection  to  the  interpretation  of  polarisation 
phenomena — and  of  the  positive  or  anodic  after-current  in 
particular — as  the  effect  of  excitation ;  the  less  so  since  the 
same  facts  which  tell  most  decidedly  in  favour  of  the  view  in 
question  can  be  observed  as  well  on  an  etherised  as  on  a  normal 
preparation.  This  applies  particularly  to  the  consequences  of 
injuring  the  ends  of  the  fibres.  In  every  case  it  may  be  de- 
monstrated that  the  appearance  of  the  positive  after-current  is 
rendered  impossible  when  the  anodic  end  of  the  muscle  has  been 
killed  by  any  means  whatever. 

The  results  of  this  discussion  may  be  summed  up  in  the  pro- 
position that  striated  muscle  under  the  influence  of  ether  vapo^ir 
falls  into  a  coiulition  in  lohich  the  application  of  an  external 
stimidus  produces  no  directly  perceptible  changes  luhether  localised  at, 
or  distant  from,  the  seat  of  excitation;  lohile,  on  the  other  hand, 
gcdvanonictric  changes,  of  equal  strength  with  those  pirodiiced  before 
narcosis,  do  appear  denionstrahly  at  the  point  of  excitation,  cdthough 
in  consequence  of  the  abolition  of  conductivity  they  are  only  loccdly 
evident. 


454  ELECTRO-PHYSIOLOGY  chap. 

The  category  of  secondary  electromotive  phenomena  is  not 
completed  with  the  admission  of  positive  anodic  and  negative 
kathodic  polarisation  in  striated  muscle.  In  view  of  the  strik- 
ing i^olar  inhibitory  effects  exhibited  under  certain  conditions, 
not  merely  in  tonically  contracted  smooth,  but  also  in  striated 
muscles  under  the  influence  of  the  battery  current,  it  is 
evident  that  the  effects  of  electrical  excitation  of  such  a  muscle 
must,  in  regard  to  secondary  electromotive  phenomena,  express 
themselves  sometimes- — under  given  conditions  —  as  positive 
kathodic,  or  negative  anodic,  after-currents.  And,  in  reality,  if  a 
muscle  with  parallel  fibres  is  conceived  as  uniformly  excited 
(contracted)  in  all  its  parts,  it  will  be  as  ineffective  in  external 
electromotive  response  as  in  the  wholly  uninjured  state  ;  if  it  is 
then  traversed  longitudinally  by  current,  relaxation  occurs 
during  closure  at  the  anode,  due  to  quelling  of  the  existing 
excitation,  while  at  the  kathode  there  will  subsequently  be  an 
increase  of  contraction.  On  opening  the  circuit  everything  is 
reversed,  and  the  inhibition  is  localised  at  the  kathode.  Then,  if 
we  picture  the  corresponding  end  of  the  muscle  as  connected  with 
the  centre  by  a  leading-off  circuit,  current  would  flow  in  the 
same  from  end  to  middle — in  the  muscle  therefore  in  the  reverse 
direction,  i.e.  in  that  of  the  polarisation  current,  i.e.  positive 
(70). 

Just  as  the  polar  inhibition  of  contraction  is  best  exhibited  in 
veratrin  poisoning,  it  is  easy  by  the  same  method  to  investigate 
the  galvanic  changes  produced  by  the  electrical  current  in  a  strip 
of  muscle,  alternately  resting  and  excited.  Instead  of  poisoning 
the  whole  muscle  with  veratrin,  it  appears  in  this  case  better  to 
apply  it  to  one  end  of  the  sartorius  only.  Each  momentary 
excitation  will  then,  as  has  already  been  pointed  out,  induce  pro- 
nounced and  tolerably  protracted  negativity  of  the  poisoned  strip. 
If  the  lower  end  of  the  sartorius  is  taken,  and  closure  of  a  de- 
scending battery  current  (2  Dan.)  effected  for  a  short  time  (1— 
4  sees.),  after  rapidly  compensating  the  veratrin  action-current 
developed  by  a  brief  excitation,  there  follows  without  exception  a 
more  or  less  eonsiderahle  swing  haek  in  the  direction  of  a  homodro- 
mous,  i.e.  ijositive,  after-current  corresijonding  with  a  passing  or 
'permanent  diminution  of  negativity  of  the  kathodic  ends  of  fibres. 
If  the  period  of  closure  is  protracted  ever  so  little,  the  effect  soon 
passes  into  its  contrary,  or  at  any  rate  becomes  diphasic  (positive, 


IV  ELECTROMOTIVE  ACTION"  IN  MUSCLE  455 

with  negative  fore-swing).  There  can  he  no  doubt  that  the  positive 
hathoclic  after -current  is  in  this  case  pt'^^ochiced  hy  an  inhibition 
{develo2)ed  at  the  'physiological  kathode  at  break  of  the  exciting 
current)  of  the  existing  persistent  excitation,  and  consequent  relaJive 
positivity  of  the  points  of  fibres  in  question. 

As  we  have  repeatedly  had  occasion  to  observe,  the  effects  of 
the  changes  in  the  excited  muscle-substance  produced  under  the 
influence  of  the  anode,  during  closure  of  the  current,  are  analogous 
in  every  particular  to  those  which  are  perceived  under  the  same 
conditions  at  the  kathode  on  opening  the  current.  This  is  true, 
not  merely  in  regard  to  change  of  form  in  the  muscle  (which  in 
both  cases  may  be  identified  as  a  localised  relaxation),  but  also  of 
the  concomitant  electromotive  phenomena,  characterised  by  relative 
positivity  of  the  entrance,  or  exit,  points  of  the  current,  by  which 
a  negative  anodic,  or  positive  kathodic,  after-current  is  produced 
respectively.  Since  the  method  of  investigating  secondary 
electromotive  phenomena  only  determines  the  consequences  of 
electrical  excitation  after  02Jening  the  polarising  current,  it  is 
evident  that — given  the  conditions  necessary  to  the  discharge 
of  a  visible  break  excitation,  e.g.  application  of  stronger  currents 
and  longer  duration  of  closure — the  positive  anodic  after-current 
which  this  produces  will  become  prominent,  while  the  negative 
after-current  only  appears  occasionally  as  a  fore-swing.  Only  in 
the  case  in  which  the  appearance  of  the  break  excitation  is 
in  any  way  hindered  or  prevented  can  we  expect  to  see  marked 
effects  in  the  direction  of  a  negative  anodic  after-current,  as,  e.g.,  in 
exhausted  preparations,  or  after  killing  the  anodic  ends  of  fibres. 

It  is  not  therefore  surprising  that  muscles  which  are 
ab  initio  in  a  state  of  persistent  excitation  (tonic  contraction) 
should  react  to  current,  both  as  regards  visible  changes  of  form 
and  galvanic  after-effects,  analogously  with  veratrinised  muscle. 
It  is  clear  that  the  phenomena  of  inhibition,  which  appear 
during  closure  at  the  anode,  on  opening  at  the  kathode,  in 
contracted  cardiac,  as  well  as  in  holothurian,  muscle,  must  corre- 
spond with  positivity  of  the  points  in  question  as  against  all 
others ;  in  the  adductor  muscle  of  anodonta  also  (which  is 
characterised  by  pronounced  tonus),  not  only  negative  anodic,  but 
also  positive  kathodic  polarisation  must  from  experimental  data 
be  reckoned  among  the  regular  consequences  of  the  passage  of  the 
electrical  current  (71). 


456  ELECTKO-PHYSIOLOGY  chAp. 

As  regards  preparations  which  are  as  far  as  possible  free  from 
tonus  (relaxed),  we  find  as  a  rule,  as  in  striated  muscle,  on  leading  off 
from  the  kathodic  end  and  middle  of  the  muscle,  that  negative 
after-currents  predominate ;  these,  in  consequence  of  the  slow 
disappearance  of  the  persistent  closure  contraction,  are  very- 
protracted,  and  are  always  most  pronounced  when  the  conditions 
are  most  favourable  to  the  closing  excitation.  On  fresher  and 
more  tonic  preparations,  on  the  other  hand,  a  positive  kathodic 
after-current  predominates  ;  it  either  appears  alone,  or  is  intro- 
duced by  a  negative  fore-swing.  Like  positive  anodic,  positive 
kathodic  polarisation  is  found  to  be  dependent  upon  the  strength 
and  duration  of  the  exciting  current,  and  increases,  generally 
speaking,  in  ratio  with  it.  There  is,  moreover,  an  alternation 
between  the  antagonistic  effects  of  polarisation  at  the  kathode 
precisely  similar  to  that  at  the  anode,  since  the  negative  after- 
current retreats  into  the  background  in  proportion  as  the  positive 
is  stronger,  and  vice  versa.  As  a  rule,  it  is  not  difficult  to  find 
in  any  given  case  a  strength  of  current  and  duration  of  closure, 
at  which  monophasic  positive  effects  alone  are  visible  on  the 
side  of  the  kathode.  But  even  then  repeated  excitation  with 
homodromous  currents  soon  brings  about  a  diphasic  action,  since 
the  positive  after-current  becomes  steadily  weaker,  with  simul- 
taneous increase  of  negative  polarisation. 

In  regard  to  the  anodic  after-current  there  is  almost  perfect 
correspondence  between  monomerous  striated,  and  smooth  mollus- 
can  muscle,  save  that  every  effect,  including  the  galvanometric 
consequences  of  excitation,  makes  its  appearance  at  a  much 
higher  current  intensity  in  the  latter.  As  a  rule  the  negative 
anodic  polarisation  of  moUuscan  muscle  increases  with  increase  in 
current  intensity,  but  only  within  a  certain  range,  beyond  which  a 
rapidly  increasing  positive  after-current  appears,  so  that  there  is 
once  more  a  diphasic  effect  with  diminishing  phase  of  negativity, 
terminating  with  a  simple  positive  variation.  This  latter,  in 
striated  muscle,  is  essentially  dependent  upon  the  actual  excitability 
of  the  preparation,  i.e.  appears  earlier,  at  less  strength  of  current 
and  duration  of  closure,  in  proportion  as  the  muscle  is  more 
excitable.  "With  regard  to  all  the  characteristics  of  positive 
anodic  polarisation — its  dependence  on  the  state  of  excitability 
of  the  preparation,  strength  and  duration  of  closure  of  the 
exciting  current,  localisation  at  the  anode,  and  greater  permanence 


IV  ELECTROMOTIVE  ACTION  IN  MUSCLE  457 

— there  can  be  no  doubt  that  it  must,  as  in  striated  muscle,  be 
regarded  solely  as  the  expression  of  the  opening  excitation.  This 
is  also  evident  from  the  fact  that  in  perfectly  fresh  and  highly 
tonic  preparations,  positive  anodic  polarisation,  like  the  persistent 
opening  contraction,  preponderates  over  the  negative  kathodic 
polarisation,  or  expression  of  the  closing  excitation  (especially 
at  the  first  stimulation) ;  the  development  of  the  positive  anodic 
after-current  is  also,  as  in  striated  muscle,  delayed  or  prevented 
by  killing  the  anodic  end  of  the  muscle. 

This  is  not  true  of  the  positive  kathodic  after-current,  which 
both  in  striated  and  smooth  muscle  is  not  merely  not  weakened, 
but  even  considerably  augmented  by  killing  the  end  of  the 
muscle. 

It  is  important  to  the  theory  of  positive  kathodic  polarisation 
that,  as  Hering  found,  there  is  sometimes,  even  in  the  perfectly 
fresh  sartorius  of  R.  esculenta,  and  still  more  in  temporaria 
(directly  after  the  first  excitation  with  the  battery  current),  a  weak 
deflection  of  the  magnet  in  the  direction  of  a  positive  kathodic  after- 
current, which  may  even  attain  a  considerable  magnitude.  A 
certain  limit  of  closure  is  essential,  as  otherwise  diphasic  or 
simple  negative  effects  are  produced.  After  killing  the  end  of 
the  muscle  corresponding  with  the  physiological  kathode,  these 
effects  are  considerably  augmented,  and  it  is  then  for  the  most 
part,  even  on  the  less  sensitive  preparations,  easy  to  produce 
tolerably  strong  positive  after-currents,  on  exciting  with  atterminal 
(admortal)  battery  currents.  They  can  thus  be  induced,  as  it 
were,  artificially,  by  killing  the  kathodic  end  of  the  muscle.  Since 
in  this  case  the  make  excitation  is  entirely  or  partially  excluded,  we 
cannot,  apart  from  other  reasons,  admit  the  interpretation  recently 
attempted  by  Locke  (17),  who  explains  the  positive  kathodic 
after-current  as  the  consequence  of  a  persistent  excitation  which  is 
longer  sustained  in  the  continuity  (middle)  of  the  muscle  than  at 
the  kathodic  end.  We  are  convinced  that  the  same  effects  appear 
when  the  sartorius  preparation  has  not  been  previously  treated 
with  physiological  salt  solution,  which,  according  to  Locke,  pre- 
disposes the  muscle  to  tetanus  contraction. 

After  due  consideration  of  all  these  facts,  and  more  especially 
of  the  striking  coincidence  between  the  conditions  of  the  entrance 
and  mode  of  manifestation  of  positive  kathodic  polarisation  in  the 
partially  veratrinised  muscle,  on  the  one  hand,  and  after  killing 


458  ELECTRO-PHYSIOLOGY  chap. 

the  kathodic  ends  of  fibre  in  normal  striated  and  smooth  muscle  in 
the  other,  we  still  believe  our  original  interpretation  to  be  the  most 
probable,  i.e.  that  here  as  there  we  are  in  face  of  a  condition 
antagonistic  to  excitation,  developed  on  breaking  the  exciting 
current  at  the  physiological  kathode,  and  a  consequent  relative 
positivity  of  the  points  at  which  current  leaves  the  muscle  to  all 
other  points  in  its  continuity. 

The  local  contraction  often  shows  macroscopically,  in  all  cases 
easily  with  the  microscope,  that  after  killing  the  ends  of  fibres  at 
one  end  of  a  normal,  regularly  constructed  muscle,  the  immediately 
adjacent  excitable  sections  of  the  same  are  in  a  condition  of  more 
or  less  pronounced  continuous  excitation. 

From  this  point  of  view,  however,  there  is  nothing  remarkable 
in  the  appearance  of  positive  kathodic  after-currents ;  they  are 
much  rather  the  immediate  and  necessary  consequence  of  every 
such  injury,  on  the  presumption  of  a  kathodic  opening  inhibition. 
Such  a  preparation  exhibits  no  essential  difference  in  its  reaction 
from  that  of  a  muscle  treated  locally  with  veratrin  immediately 
after  a  momentary  stimulus. 

The  last  question  to  be  discussed  is  how  we  are  to  conceive 
of  positive  kathodic  polarisation  in  the  normally  uninjured,  current- 
less  muscle.  Locke's  theory  (I.e.),  which  refers  it  to  a  surplus  of 
excitation  near  the  centre  of  muscles  treated  with  NaCl,  has 
already  been  considered.  We  regard  it  as  answered  by  identical 
experiments  on  perfectly  fresh,  non-moistened  preparations. 

The  positive  kathodic  after-current  which  then  appears  under 
certain  conditions,  cannot  be  forthwith  compared  with  the  cor- 
responding effect  in  the  uninjured  molluscan  muscle ;  for  in  the 
last  case  we  have  a  tissue  which  is  in  every  part  in  a  state  of  con- 
tinuous (tonic)  excitation,  while  in  normal  striated  muscle  this  is 
not  so.  If  in  the  first  we  find  only  the  consequences  of  a 
quelling  of  the  tonic  excitation,  appearing  at  definite  points, 
and  a  consequent  relative  positivity  of  those  points,  in  the  second 
we  are  forced  to  take  into  account  a  local  alteration  of  the 
"  resting  "  muscle-substance,  as  exhibited  in  the  given  instance  by 
a  positivity  of  the  same  towards  other  unaltered  points  of  fibres. 
As  we  see  at  once,  such  a  change  at  the  kathode  can,  under  the 
obtaining  conditions,  be  regarded  only  as  the  consequence  of  the 
previous  make  excitation,  through  which  the  same  points  of  fibres 
undoubtedly  become  strongly  negative  ;  so  that  we  are  forced  into 


n'  ELECTROMOTIVE  ACTION  IN  MUSCLE  459 

the  conclusion  that  there  is  here,  as  it  were,  a  reaction  of  the 
living  substance  towards  the  preceding  excitation. 

The  results  arrived  at  in  the  previous  discussion  of  the  visible 
effects  of  electrical  excitation  in  cardiac  muscle,  as  also  in  differ- 
ent smooth  muscular  parts  (holothurian  and  echinus  muscle), 
are  essentially  confirmed  and  elucidated  by  these  secondary 
electromotive  phenomena.  For  they  establish  with  certainty  the 
general  vahdity  of  those  conclusions  to  which  (more  particularly) 
the  observations  on  the  effects  of  excitation  on  cardiac  muscle 
in  a  state  of  alternating  contraction  had  pointed. 

The  theory  of  two  inhibitory  processes  antagonistic  to  the 
polar  processes  of  excitation,  which  we  found  to  be  inevitable 
re  cardiac  muscle  in  systole,  now  proves  to  be  the  simplest 
explanation  of  the  consequences  of  electrical  excitation  of  striated 
skeletal  muscle.  This  is  equally  true  of  the  mechanical  effects 
of  excitation,  and  of  the  electromotive  after-effects.  The  two 
methods  of  investigation,  whether  by  testing  the  changes  of 
form  in  the  excited  muscle,  or  by  ascertaining  the  state  of 
polarisation  at  the  end  of  excitation,  complete  themselves 
reciprocally,  so  that  a  satisfactory  view  of  the  nature  of  the 
changes  due  to  current  is  first  obtained  from  the  combination  of 
both  methods.  We  must  especially  remark  that  a  direct  proof 
of  the  existence  of  an  antagonistic  process,  following  or  preceding 
the  excitation,  as  expressed  in  corresponding  changes  of  form  in 
the  muscle,  is  obviously  possible  only  during  pre-existing  persist- 
ent contraction,  but  may  in  other  cases  be  concluded  very 
indirectly,  e.g.  by  examination  of  the  alterations  of  excitability. 
On  the  other  hand,  the  investigation  of  secondary  electromotive 
phenomena  gives  positive  evidence  of  the  existence  of  polar 
antagonistic  processes  in  the  resting  muscle  also. 

In  conclusion,  the  positive  anodic  and  negative  kathodic 
after -current  on  the  one  hand,  the  positive  kathodic  and 
negative  anodic  after-current  on  the  other,  are  due  respectively 
to  the  antagonistic  polar  alterations  of  the  muscle-substance,  one 
of  which  tends  to  negativity,  the  other  to  positivity,  of  the 
points  of  fibres  implicated.  To  the  former  correspond  (as 
mechanical  effects  of  excitation)  the  closing  and  opening  con- 
traction, to  the  latter  (where  this  is  a  tonic  state  of  contraction) 
the  closing  and  opening  relaxation.  The  one,  like  the  other,  is 
conditioned    by    chemical  alterations    in    the    excitable   muscle- 


460  ELECTRO-PHYSIOLOGY 


substance,  arising  under  the  injQuence  of  current,  as  to  the 
nature  of  which  nothing  definite  can  at  present  be  predicated. 
But  while  the  changes  consequent  upon  closure  of  the  current 
are  directly  engendered  by  the  latter,  the  opening  effects  relate 
essentially  to  phenomena  of  reaction  in  the  altered  muscle- 
substance  itself,  and  not  merely  the  anodic  opening  excitation, 
but  the  kathodic  opening  inhibition  also,  must  be  interpreted 
in  this  sense. 


CHAPTEE   V 

ELECTEOMOTIVE    ACTION    OF    EPITHELIAL    AND    GLAND    CELLS 

Even  in  the  muscle  it  is  not  possible  to  make  any  sharp 
separation  between  "  current  of  rest "  and  "  current  of  action," 
seeing  that  both  manifestations  are  to  a  certain  extent  distinct 
in  degree  only,  and  still  less  can  this  be  effected  with  regard 
to  the  electromotive  action  of  other  animal  and  plant  cells,  in 
which  differences  of  potential  (irrespective  of  whether  they 
appear  ]3efore  or  during  artificial  excitation,  and  are  relatively 
altered  in  one  or  the  other  direction)  are  always  and  solely  the 
expression  of  chemical  dissimilarity  in  adjacent  parts  of  the  living 
continuum.  From  this  point  of  view  therefore  it  is  purely  arbi- 
trary, and  indeed  illegitimate,  to  speak  of  the  "rest  current" 
of  a  glandular,  mucous  membrane,  or  vegetable  cell-aggregate,  in 
contradistinction  to  the  current  of  action,  since  in  both  cases 
we  have  a  reaction  deriving  from  the  same  cause,  i.e.  the 
presence  of  certain  chemical  processes  of  metabolism  at  given 
points  of  the  mass  of  protoplasm,  which  are  only  altered 
quantitatively  or  qualitatively,  by  direct  or  indirect  excitation. 
This  does  not  of  course  exclude  the  event  that  with  initial 
absence  of  current  in  such  parts,  differences  of  potential  may  be 
first  called  out,  as  in  "  parelectronomic  "  muscle,  by  excitation. 

It  is  therefore  advisable  to  treat  the  electromotive  reactions 
of  glandular  and  epithelial  cells  together,  without  separating 
the  discussion  of  the  effects  which  appear  during  rest  and 
during  action,  as  was  convenient  in  muscle.  It  is  perhaps 
a  consequence  of  the  difficulties  which  the  long -prevail- 
ing molecular  theory  threw  in  the  way  of  any  systematic 
account  of  the  facts  under  consideration,  that  the  experimental 
treatment  of  this  part  of  the  field  is  quite  disproportionate  to 


462  ELEGTKO-PHYSIOLOGY  chap. 

the  development  of  muscle  and  nerve  physics,  although  some 
fundamental  researches  date  as  far  back  as  the  discovery  of  the 
muscle  current. 

There  was  for  long  a  certain  disinclination  to  attribute 
electromotive  activity  to  cells  of  which  a  regular  mole- 
cular structure,  comparable  with  that  of  muscle,  could  not  be 
predicated.  Engelmann  (72)  in  1872,  during  a  discussion  as 
to  whether  the  electromotive  action  of  the  frog's  skin  should 
be  referred  to  the  glandular  epithelium,  expressed  his  reluctance 
"  to  assume  in  cells  which,  like  those  before  us,  exhibit  no  sign 
of  regular,  axial  arrangement  of  the  particles,  any  regular, 
electromotive  structure  capable  of  giving  external  visible 
response,"  and  maintained  that  the  gla.nd-m2iscles  were  the  sole 
effectual  source  of  the  electrical  currents  within  the  glandular 
layer. 

As  we  have  seen,  du  Bois-Keymond,  whose  name  once 
more  heads  these  investigations,  was  led  by  his  attempts  to 
demonstrate  the  supposed  current  of  rest  in  uninjured  muscles 
in  situ  through  the  skin,  to  the  discovery  of  the  marked  electro- 
motive activity  of  the  frog's  skin.  On  bringing  any  two  points 
of  the  uninjured  surface  of  a  piece  of  excised  skin,  stretched  on  a 
glass  plate,  with  leading -off  pads  of  salt  clay,  into  unequal 
contact,  he  always  obtained  a  current  which  flowed  within  the 
skin  from  the  pad  last  applied  to  the  other.  When  both  pads 
were  applied  as  nearly  as  possible  simultaneously,  the  needle 
remained  at  rest — comparatively  speaking. 

Du  Bois-Eeymond  at  once  recognised  that  this  effect  was  pro- 
duced by  the  non- simultaneous  contact.  "  Each  point  of  contact 
is  the  seat  of  electromotive  force  in  the  direction  of  pad  to  skin,  i.e. 
inwards  ;  but  the  contact  of  the  salt  solution  acts  at  the  same  time 
upon  the  cause  of  the  electrical  impulse.  IJence,  with  dissimilar 
contact,  there  is  a  current  in  the  direction  of  impulse  from  the  last 
point  of  contact,  which  continues  until  the  difference  in  impulse 
at  the  two  points  becomes  negligible."  Du  Bois-Keymond 
next  obtained  much  stronger  deflections  on  leading  off  from  the 
external  and  internal  skin  surface,  always  indeed  in  the  direction 
from  the  former  to  the  latter.  Here,  too,  the  impulse  was  soon 
abolished  by  salt  solution,  and  was  ah  initio  nil  when  the 
surface  of  the  skin  was  painted  with  NaCl  before  leading  off 
from  it.      The  current  was  equally  neutralised  by  scraping  off  the 


V      ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      463 

epithelial  and  glandular  layer.  Since  du  Bois-Eeymond  found 
the  skin  current  particularly  strong  in  the  toad,  where  the 
skin  glands  are  vigorously  developed,  while  the  glandless  skin 
of  fishes  (eel,  tench,  pike,  perch)  appeared  entirely  devoid  of 
current,  the  presumption  was  "  that  the  electromotive  activity 
of  the  skin  is  in  relation  with  the  special  dermic  secretions 
peculiar  to  the  naked  amphibians."  This  view  subsequently 
obtained  substantial  support  from  the  observations  of  Rosenthal 
(75)  and  Eober  (76).  The  former  found  not  merely  that  the 
skin  glands  of  the  frog  and  other  naked  amphibians  are  the 
seat  of  electromotive  forces,  directed  invariably  from  mouth 
to  fundus,  but  that  the  same  holds  good  of  the  mucous  glands 
of  the  stomach,  so  that  these  electromotive  forces  "  may  with 
great  probability  be  regarded  as  an  essential  property  of 
glandular  substance,  just  as  we  are  accustomed  to  reckon 
electromotive  forces  among  the  essential  vital  manifestations  of 
nerve  and  muscle." 

This  view  is  opposed  to  a  later  theory  brought  forward  by 
Engelmann  (72,  p.  97),  according  to  which  the  "gland  currents" 
in  question  are  of  "  myogenic "  origin,  initiated  by  the  layer  of 
contractile  fibre-cells  which  surround  each  glandular  body  exter- 
nally. Engelmann  tried  to  make  good  this  interpretation,  which 
of  course  stands  and  falls  with  the  pre-existence  theory,  from  a 
long  series  of  excellent  observations,  to  which  we  shall  frequently 
liave  occasion  to  return  in  the  sequel.  Yet  it  is  incontestable 
that  even  from  the  standpoint  of  the  pre-existence  theory,  the 
reaction  of  the  skin  current  of  the  frog  tells  against  rather  than 
for  Engelmann's  hypothesis. 

Hermann,  again,  proposes  "  that  it  is  not,  or  not  pre-eminently, 
the  glands,  but  the  eijithelial  layer  which  is  (during  rest)  the  seat 
of  electromotive  skin  action."  The  reasons  which  originally 
compelled  du  Bois-Eeymond  to  regard  the  glands  as  the  essential 
cause  of  the  skin  currents  in  naked  amphibia,  i.e.  absence  of  the 
same  in  the  "non-glandular"  skin  of  fishes,  were  believed  by 
Hermann  to  be  put  out  of  court  by  the  demonstration  of  a  regular, 
ingoing  skin  current  in  a  great  number  of  the  fishes  examined 
(75).  To  this  it  might  certainly  be  objected  that  the  skin  of  the 
fish  is  not  really  glandless,  but  contains  innumerable  unicellular 
mucous  glands  ("  goblet  cells "),  which  in  many  cases  may  be 
regarded    as    one    large,    superficially    flattened,    mucous    gland 


464  ELECTRO-PHYSIOLOGY  chap. 

(cf.  F.  E.  Schultze,  78).  And  since  we  know  that  neither  morpho- 
logically, nor  with  regard  to  physiological  function,  is  there  any 
fundamental  difference  between  uni-  and  multicellular  mucous 
glands,  it  is  natural  to  regard  the  rest  current  of  the  fish's  skin  as 
referable  to  the  goblet  cells  which  function  as  unicellular  glands. 
Hermann  actually  does  this  when,  in  terms  of  the  alteration 
theory,  he  reckons  each  partial  mucin  metamorphosis  of  single 
cells,  as  well  as  the  elements  of  the  secretory  glands,  as  a  source 
of  regular  electromotive  action,  a  force  "  which,  entering  by  the 
free  epithelium,  is  directed  in  the  gland  from  lumen  to  matrix." 
Such  currents  are,  in  fact,  demonstrable  wherever  mucin - 
forming  cells,  or  glands,  are  present  (skin  of  fish  and  naked  am- 
phibia, tongue,  mucous  membrane  of  throat,  stomach,  and  cloaca). 
And  that  electromotive  action  may  further,  in. Hermann's  sense, 
be  predicated  of  other  non-glandular  epithelial  cells  seems  to  be 
established  by  the  recent  researches  of  E.  Waymouth  Eeid  (88). 

Seeing  that,  with  the  exception  of  the  plant  currents  to  be 
considered  later,  the  experimental  data  of  "  cell  currents "  are 
founded  almost  solely  upon  electromotive  action  in  uni-  and 
multicellular  mucous  glands,  the  details  of  these  observations 
must  be  examined  a  little  more  closely.  The  most  appropriate 
object  for  experiment  is  perhaps  the  tongue  of  the  frog,  with  its 
wealth  of  goblet  cells  and  mucous  glands,  in  which,  moreover,  it 
is  easy  to  expose  the  secretory  nerves.  As  regards  the  opinion 
expressed  by  Engelmann  (supra)  of  the  origin  of  skin  currents, 
it  is  notable  that  the  lingual  glands  containing  characteristic 
mucous  cells  lie  free  of  muscle  in  the  connective  tissue  immediately 
under  the  surface,  the  papillae  of  which  are  covered  with  a  single- 
layered  epithelium  consisting  of  goblet  and  ciliated  cells.  The 
mucous,  viscous  content  of  the  glandular  membrane  is  everywhere, 
as  appears  from  transverse  sections,  in  direct  connection  with  the 
mucous  layer  covering  the  surface  of  the  tongue,  as  we  should 
expect  from  the  wide  mouth  of  the  glands.  The  epithelium  of 
the  under  surface  of  the  tongue,  turned  to  the  floor  of  the  mouth, 
is  also  rich  in  goblet  cells. 

Various  methods  may  be  employed  to  investigate  the  "  current 
of  rest "  in  the  tongue,  as  will  presently  be  described.  Speaking 
generally,  we  may  picture  the  surface  of  the  tongue  as  a  freely 
and  irregularly  folded  surface,  covered  in  its  whole  extent  with  a 
single  layer  of  secretory  cells,  intermixed  sparsely  with  ciliated 


V      ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      465 

cells.  The  glands  thus  appear  merely  more  or  less  deeply  pitted 
in  the  continuity  of  the  layer  of  cells,  from  the  inner  surface  of 
which  it  is  possible  to  lead  off,  since,  as  was  said  above,  the 
secretory  layer  covering  the  tongue  is  nearly  everywhere  in  direct 
connection  with  the  fluid  contents  of  the  glandular  membrane. 
If  the  tongue  is  excised  at  the  root,  and  stretched  upon  any 
indifferent  conducting  surface,  such  as  a  block  of  salt  clay,  we 
shall  obviously  have  to  test  the  electromotive  action  of  the 
epithelium  of  the  whole  upper  surface  (which  clothes  not  only 
the  glands  but  also  the  .  papillae  lying  between  them),  even  if 
the  inferior  surface  of  the  tongue  were  not  invested  with  a  simi- 
larly constructed,  even  layer  of  cells,  the  single  elements  of  which 
are  generally  placed  symmetrically  with  those  of  the  upper 
surface.  Between  the  two  lies  a  thick  layer  of  connective 
tissue  and  striated  muscle,  which,  under  normal  circumstances, 
must  be  regarded  as  non-electromotive. 

In  every  case,  therefore,  it  is  possible  to  lead  off  from  the 
basal  part  of  the  individual  cell-elements  of  the  upper  and  lower 
surface  of  the  tongue.  On  the  assumption  of  a  perfectly  equal 
electromotive  action  of  the  epithelium  of  both  surfaces  (a  hypo- 
thesis which  must,  however,  be  excluded  on  account  of  the  very 
different  mass -relations  of  the  cell  layers  in  question),  there 
would,  of  course,  be  no  effect  on  leading  off  from  two  symme- 
trically opposed  points  of  the  upper  and  lower  surface.  The  web 
of  the  frog's  hind-leg,  e.g.,  on  leading  off  from  both  sides,  gives 
only  weak  and  irregular  electrical  effects  on  account  of  its 
symmetrical  structure.  The  tongue,  on  the  contrary,  under  the 
same  conditions,  yields  almost  invariably  a  strong  current  directed 
in  the  leading -off  circuit  from  under  to  upper  surface,  i.e.  an 
"  entering "  current  in  Hermann's  sense,  which  often  sends  the 
scale  far  out  of  the  field  of  vision.  Since,  as  will  be  gathered 
from  the  following,  the  lingual  currents  undergo  very  considerable 
alteration  from  the  most  insignificant  mechanical  impacts,  it  is 
essential  to  proceed  with  great  caution,  avoiding  the  slightest 
pull  or  contact.  The  following  was,  in  our  experiments,  the 
most  convenient  method  of  leading  off  from  the  excised  tongue, 
through  which  blood  is  no  longer  circulating.  The  frog  was 
weakly  curarised,  until  it  just  lost  power  of  movement ;  the 
external  skin  was  then  carefully  removed  along  the  whole  region 
of  the  lower  jaw,  to  exclude  any  possible  complication  from  its 

2  H 


ELECTRO-PHYSIOLOGY 


electromotive  action, — the  jaw  was  exarticulated  and  divided 
by  a  sharp  cut  below  the  apex  of  the  tongue.  It  is  true  that 
muscles  are  injured  by  this  method,  and  that  current  may  diffuse 
from  their  stumps  into  the  galvanometer  circuit ;  but  the  efiect 
of  this  is  practically  negligible  against  the  force  of  the  lingual 
current,  as  shown  by  control  experiments  in  the  same  preparation 
when  the  tongue  has  been  removed.  The  lead-off  is  accomplished 
as  follows :  the  lower  jaw,  with  its  under  surface,  is  placed  on  a 
block  of  salt  clay  of  corresponding  proportions,  which  admits  of 
a  lead-off  from  the  lower  side  of  the  tongue,  by  the  floor 
of  the  mouth,  when  one  brush- electrode  is  brought  into  contact 
with  it,  while  the  other  is  applied  to  any  given  point  of  the 
upper  lingual  surface.  It  should  be  noticed  that  the  floor  of  the 
mouth  on  which  the  tongue  is  lying  is  itself  invested  with  a 
mucosa,  rich  in  goblet  cells,  and  therefore  gives  electromotive 
reaction.  But  if  the  tongue  is  cut  out  at  the  root,  and  the  lead- 
off  effected  as  before  from  the  clay  block  and  surface  of  the 
mucous  membrane,  which  had  previously  been  covered  by  the 
tongue,  there  will  usually  be  very  slight  deflections  only,  in  one 
or  the  other  direction,  so  that  the  disturbance  is  negligible. 

There  can  thus  be  no  doubt  that,  however  the  lead-off  from 
the  tongue  is  effected,  the  results  observed  are  produced  respect- 
ively by  the  electromotive  activity  of  the  surface  einthelium  in  its 
widest  sense  (epithelium  of  glands  and  papillse),  even  if  the 
absolute  intensity  of  this  latter  is  modified  to  a  degree  that 
cannot  always  be  exactly  determined,  by  the  unavoidable  in- 
clusion, on  leading  oft',  of  other  electromotive  elements.  This  is 
most  clearly  shown  in  the  fact,  that  (in  every  experiment  arranged 
as  above)  the  current,  which  sometimes  makes  a  very  vigorous 
entrance,  driving  the  scale  far  out  of  the  field  of  vision,  dwindles 
after  destruction  of  the  surface  epithelium  into  irregular  traces, 
though  neither  the  epithelium  of  the  under  surface  of  the  tongue, 
nor  that  of  the  floor  of  the  mouth,  can  be  perceptibly  affected  by 
it.  On  the  other  hand,  it  is  easy  to  ascertain  that  even  little 
scraps  of  mucosa,  snipped  out  with  a  flat  scissor-cut  from  the  surface 
of  the  frog's  tongue,  and  examined,  after  a  short  rest,  on  a  bed  of 
salt  clay,  are,  just  as  much  as  the  tongue,  the  seat  of  a  strong 
ingoing  current.  Thus  we  may  regard  it  as  certain  that  the 
normal  current  of  rest  in  the  tongue  is  essentially  clue  to  the 
electromotive  action  of  the  surface  epithelium,  its  glands  included. 


V      ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      467 

As  regards  the  strength  of  the  "  rest  current "  under  various 
conditions,  a  very  brief  observation  of  the  object  in  question  makes 
it  plain  that  the  electromotive  reaction  is  far  more  dependent 
upon  external  accidents  and  internal  changes  than  is  the  case 
with  the  muscle  current.  The  individuality  of  the  frog,  its  state 
of  nutrition,  temperature  relations,  the  time  of  year,  and  other 
circumstances,  affect  the  currents  of  the  mucosa  so  strongly  that 
the  results  are  extremely  variable. 

On,  comparing  the  muscle  current  with  that  of  the  lingual 
mucosa,  the  most  striking  point  is  the  great  inconstancy  of  the 
latter,  apparent  in  every  kind  of  lead-off — most  of  all,  however, 
by  Hermann's  method  (suprct)  of  leading  off  from  the  uninjured, 
weakly  curarised  frog  at  the  upper  surface  of  the  tongue,  and 
any  indifferent  portion  of  the  body  (from  which  the  skin 
has  been  removed,  but  which  is  otherwise  totally  uninjured), 
such  as  the  muscles  of  the  thigh  or  leg.  If,  under  these  con- 
ditions, the  entering  "  current  of  rest "  is  at  all  vigorous,  the 
scale  will  hardly  remain  at  rest  for  a  moment  after  compensa- 
tion, but  swings  in  the  direction  of  now  increase,  now  decrease, 
of  the  existing  current.  These  oscillations,  which  are  sometimes 
merely  indicated,  may  in  other  cases  extend  over  many  degrees 
of  the  scale,  while  during  the  observation  the  current  of  rest 
may  take  up  a  perfectly  different  mean.  Sometimes  the  antagonistic 
deflections  occur  with  a  tolerably  regular  rhythm,  but  in  most 
cases  this  is  not  recognisable.  The  possibility  that  the  lingual 
glands  may,  as  has  been  shown,  be  innervated  from  the  central 
organ,  suggests  that  the  effects  described  may  be  due  to  a  central 
excitatory  impulse ;  the  oscillations,  however,  also  appear,  though 
as  a  rule  feebly,  in  the  preparations  of  the  lower  jaw  described 
above,  so  that  m  any  case  their  immediate  cause  must  be  sought 
in  the  tongue  itself. 

If  the  lingual  rest  current  is  led  off  as  above  from  the  whole 
uninjured  frog,  the  lower  jaw  being  drawn  back  as  far  as  possible 
by  means  of  a  thread  passed  through  close  to  the  tongue,  while 
the  animal  lies  on  its  back,  the  current,  immediately  after  applying 
the  electrodes,  is  almost  invariably  found  to  be  rapidly  increasing, 
and  it  may  happen  that  a  current  which  is  extremely  weak  when 
the  throat  is  first  opened,  will  drive  the  scale  out  of  the  field  a 
few  minutes  later.  On  taking  off  and  replacing  the  electrode  in 
contact  with  the  surface  of  the  tongue,  at  the  same  or  any  other 


468  ELECTRO-PHYSIOLOGY 


point,  a  regular  diminution  may  be  observed,  with  subsequent 
increase  of  current.  The  explanation  of  these  effects  can  only 
be  given  in  connection  with  other  facts  to  be  communicated  later. 
The  marked  effect  produced  by  changes  of  temperature  upon 
the  electromotive  action  of  the  frog's  tongue  claim  fuller  dis- 
cussion. If  a  curarised  frog  is  kept  for  a  long  period  (several 
hours)  at  a  low  temperature,  the  tongue,  if  examined  as  quickly 
as  possible,  will  often  exhibit  a  reversed,  i.e.  outgoing  current  of  rest, 
which  is  frequently  no  less  strong  than  the  previous  normal 
incoming  current.  As  a  rule,  this  reversed  current  diminishes 
pretty  quickly  as  the  preparation  gets  warmer.  A  short  stage 
occurs  when,  under  the  given  conditions  of  leading  off  (surface 
of  tongue  and  exposed  muscles  of  leg),  no  difference  of  potential  is 
visible,  after  which  the  normal  entering  current  gradually  develops. 
The  strongest  reversed  effects  are  obtained  when  weakly  curarised 
frogs  are  packed  in  snow  for  some  hours.  If  the  lingual  current 
is  then  investigated  as  above  in  the  uninjured  animal  as  quickly 
as  possible,  before  any  heat  effect  becomes  visible,  an  extraordin- 
arily strong  deflection,  far  exceeding  the  scale,  may  often  be 
seen  in  the  direction  of  an  outgoing  current.  And  if  such  a  "  cold 
frog"  is  left  in  a  warm  room,  the  normal  entering  current  will 
develop,  as  has  been  shown,  more  or  less  quickly.  These 
experiments  led  to  the  further  testing  of  heat  and  cold  upon  the 
excised  tongue,  using  throughout  the  preparation  from  the  lower 
jaw.  Since  0*5  %  NaCl  solution  was  found  to  be  tolerably 
indifferent  for  electromotive  action  of  the  tongue,  immersion 
for  hours  in  this  fluid  producing  no  noticeable  effect,  the  simplest 
method  of  warming  or  cooling  appeared  to  be  to  place  the 
preparation  in  solutions  of  the  same  molecular  strength  at 
different  temperatures.  And  this  showed,  without  exception, 
that  every  preparation  that  had  previously  acted  strongly  in  the 
normal  direction  now  became  currentless  in  the  shortest  possible 
interval,  developing  indeed  in  most  cases  a  reversed  (outgoing) 
current,  provided  it  were  placed  on  snow  in  a  watch-glass  filled 
with  physiological  salt  solution,  and  covered  with  a  bell-glass  for 
some  hours  at  low  temperature  (0—2°  C.)  The  same  result  is 
also  obtained  if  the  preparation  on  the  clay  block  is  simply 
placed  for  several  hours  in  a  moist  chamber  in  a  cold,  but  not 
frosty,  room  (at  about  2—4°  C.)  In  every  case  the  outgoing 
current    of  rest   can  be  reversed   almost  instantaneously  if  the 


V      ELECTROMOTIVE  ACTION  OF  EPITHELIAL  A.jSTD  GLAND  CELLS      469 

preparation  is  immersed  in  physiological  salt  solution  at  about 
20—30°  C.  These  experiments  involuntarily  recall  Matteucci's 
statement  of  the  effect  of  cooling  upon  the  muscle  current. 
Without  denying  this,  we  must  however  point  out  the  enormous 
difference  in  degree  which  is  apparent  in  either  direction,  in  the 
two  cases.  The  "  rest  current "  of  the  muscle  (i.e.  the  demarca- 
tion current  of  Hermann)  is  certainly  weakened  by  intense  cool- 
insj,  but  is  never  abolished,  much  less  reversed  in  direction. 

We  have  found  that  preparations  of  the  tongue,  which,  when 
freshly  examined,  exhibit  strong  electromotive  action  in  the  normal 
direction,  afford  reversed  currents  less  readily  on  cooling  than 
those  whose  activity,  from  long  immersion  at  a  not  unduly  high 
temperature,  is  already  considerably  diminished.  Thus  we  found 
throughout  that  the  frogs  best  suited  to  these  experiments  had  in 
every  case  been  kept  for  a  long  time  during  the  winter  in  a  warm 
room.  "  Cold  frogs  "  nearly  always  afforded  preparations,  which  if 
freshly  examined  gave  very  strong  and  comparatively  constant 
currents,  opposing,  as  it  were,  a  greater  resistance  to  the  influence 
of  cooling  than  the  equally  strong,  or  even  stronger,  rest  currents 
of  "  warm  frogs."  With  this  may  perhaps  be  connected  the  fact  that 
spring  frogs  packed  in  snow  usually  yield  a  much  stronger  out- 
going lingual  current  than  winter  frogs.  The  latter,  however, 
according  to  our  experiences,  may  be  easily  thrown  into  a 
similarly  favourable  disposition,  if  they  are  kept  for  two  or  three 
days  before  the  experiment  in  a  warm  room  near  the  stove.  Then 
on  leading  off  the  tongue  current  the  deflection  obtained  will 
often  be  as  marked,  in  the  same  direction,  as  in  cold  frogs,  only  it 
is,  so  to  speak,  in  labile  equilibrium.  On  cooling,  it  gives  way 
much  more  quickly  to  the  opposite  current  than  in  fresh,  cold 
frogs,  where  it  is  sometimes  quite  impossible  to  abolish  the 
normal  entering  current  by  the  methods  of  cooling  described 
so  far. 

This  does,  however,  occur  without  exception,  if  melting  snow 
or  ice  is  brought  into  direct  contact  with  the  surface  of  the 
mucosa,  and  we  have  never  met  with  a  case  in  which,  under 
such  conditions,  there  was  not  a  real  reversal  of  the  normal  rest 
current.  In  detail,  however,  the  reaction  in  different  preparations 
varies  considerably  in  its  proportions,  wherein  the  effect  of  the  con- 
ditions already  cited  is  once  more  evident.  We  have  found  it  most 
convenient  to  introduce  small,  even  plates  of  ice — not  too  thick 


470  ELECTRO-PHYSIOLOGY 


(as  may  easily  be  obtained  by  freezing  thin  layers  of  water) — 
as  carefully  as  possible  between  the  tongue  and  the  leading-off 
electrode.  The  current  will  then  sink  almost  instantaneously  to 
zero,  and  is,  as  a  rule,  reversed  in  a  few  seconds.  The  new  out- 
going current  may  sometimes  be  of  such  dimensions  that  the  scale 
flies  out  of  the  field.  If  the  single  application  of  ice  is  not 
sufiicient,  repetition  of  the  treatment  is  sure  to  be  success- 
ful. After  the  ice  has  melted,  the  reversed  current  generally 
diminishes  rapidly,  and  finally  turns  round  again  as  an  entering 
current.  The  diminution,  which  occurs  more  rapidly  at  first  than 
later,  is  not  always  uniform,  but  takes  place  with  more  or  less 
considerable  oscillations. 

If  the  facts  previously  communicated  are  decidedly  in  favour 
of  the  view  that  we  here  have  mainly  an  effect  of  cooling,  the 
obvious  objection  must  be  answered  that  contact  of  the  electrode 
with  the  melting  ice  might  give  rise  to  a  "  thermo-current."  This 
conjecture  is  the  more  probable,  since  currents  are  actually  known 
to  exist  in  consequence  of  the  unequal  warmth  of  the  leading-off, 
unpolarisable  electrodes.  Not  merely  are  important  thermo- 
electric effects  caused  by  unequal  temperature  in  the  two  tubes 
containing  the  glass-rods,  but — as  found  by  Worm-Miiller  and 
verified  by  Griitzner — a  weaker  "  thermo-current,"  reversed  in  direc- 
tion, may  also  arise  between  the  clay  plug  saturated  with  ISTaCl 
solution,  and  the  solution  of  zinc  sulphate.  It  passes  from  zinc 
sulphate  to  clay,  with  an  E.M.F.  of  0-002  Dan.  at  35°  difference 
of  temperature.  Control  experiments,  effected  for  the  most  part 
with  the  clay  block  alone,  as  well  as  with  dead,  electrically  in- 
effective preparations  of  the  tongue  placed  upon  it,  gave  only 
weak  deflections  in  the  same  direction  as  before  the  experiments 
in  question,  i.e.  the  cooled  electrodes  were,  so  to  speak,  weakly 
positive.  There  is  not,  however,  the  smallest  reason  to  refer  the 
very  marked  action  of  normal  preparations  to  this  cause.  Apart 
from  all  the  other  reasons  that  have  been  given,  it  is  only 
necessary  to  point  out  that  the  full  effect  of  the  outgoing  current 
appears  also  in  the  case  in  which  the  brush -electrode  is  first 
brought  into  contact  with  the  tongue  some  time  after  it  has  been 
laid  upon  ice  (after  removing  the  water  of  liquefaction),  when  a 
marked  deflection  at  once  follows  in  the  expected  direction,  and 
finally  drives  the  scale  off  the  field — which  can  hardly,  in  this 
case,  correspond  with  any  difference  in  temperature.      Moreover, 


V      ELECTROJIOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      471 

in  preparations  of  the  lower  jaw,  which  by  alternate  freezing  and 
thawing  had.  been  rendered  perfectly  currentless,  and  had  lain  for 
some  time  in  salt  solution  warmed  to  the  temperature  of  the  room, 
even  repeated  application  of  snow  or  ice  leaves  hardly  any  trace 
of  an  outgoing  current. 

From  these  observations  we  may  take  it  as  proved  that  the 
regular  entering  current  of  the  mucous  membrane  of  the  frog's 
tongue  is  not  merely  diminished  to  zero  with  extreme  rapidity 
when  sufiiciently  cooled,  but  may  also  be  reversed — when  the 
reversed  current,  under  some  conditions,  reaches  the  same  pro- 
portions as  those  of  the  original  "  normal "  current. 

In  the  experiments  last  quoted,  the  surface  of  the  lingual 
mucosa  was  moistened  with  the  water  of  the  melting  ice,  so  that 
it  became  necessary  to  consider  whether  the  results  of  the  experi- 
ment were  not  due,  at  least  in  part,  to  this  factor.  That  it  was 
certainly  not  the  main  cause  is  amply  proved  by  the  facts  above 
stated,  but  the  strikingly  rapid  reversal  of  the  current,  as  well  as 
its  E.M.F.,  might  be  partially  due  to  a  water  effect.  We  accordingly 
examined  the  effect  of  the  varying  bulk  of  water  on  the  electro- 
motive properties  of  the  lingual  mucosa  during  "  rest."  Engel- 
mann  (72)  had  already  made  an  excellent  series  of  observations 
with  the  same  object  on  the  skin  of  the  frog,  to  which  we  shall 
return  later.  These  relate  to  the  action  of  water,  and  of  different 
concentrations  of  salt  solution,  upon  the  equally  ingoing  current 
of  rest  in  the  skin.  Since,  as  we  shall  find,  there  is  in  every 
respect  almost  complete  agreement  between  the  electromotive 
action  of  the  external  skin,  and  the  tongue,  of  the  frog,  it  might 
be  assumed  a  priori  that  the  same  would  be  the  case  with  regard 
to  the  effects  of  addition  and  subtraction  of  water.  Owing 
to  the  extraordinary  sensitivity  of  the  lingual  mucosa  {infra)  to 
the  slightest  mechanical  stimulus,  the  fluid  to  be  tested  must 
not  simply  be  poured  on,  or  applied  with  the  brush  (which  would 
easily  lead  to  the  worst  fallacies),  but  the  preparation  must  be 
dipped  into  watch-glasses  containing  the  required  solutions. 
After  a  shorter  or  longer  bath,  the  lingual  current  is  tested  again, 
as  described  above,  by  leading  off  from  a  clay  bed  and  the 
surface  of  the  mucosa.  While  normal  0'6  %  JSTaCl  solution 
is  indifferent  for  the  tongue  also,  in  so  far  that  the  power  of 
giving  electromotive  reaction  will  persist  for  hours  and  even  days 
if  the  temperature  is  not  too  high,  the  E.M.F.   of  the  ingoing 


472  ELECTRO-PHYSIOLOGY  chap. 

mucosa  current  is  always  considerably  increased  if — after  the 
deflection  has  been  rendered  approximately  constant  by  long 
immersion  in  ordinary  physiological  saline — a  semi-normal  (i.e. 
0"2-0'3  ^)  NaCl  solution  is  applied  :  still  more  so  if  spring 
water  or  distilled  water  is  employed. 

A  single  drop  of  distilled  water  applied  with  the  leading- 
off  electrode  to  the  surface  of  a  tongue  previously  treated  with 
physiological  salt  solution  is  sufficient  to  produce  a  strong  positive 
variation  of  the  mucous  current,  although  the  resistance  in  the 
circuit  of  course  increases  considerably.  Even  long  immersion  in 
spring  water  not  merely  fails  to  weaken  the  normal  current,  but 
may  even  maintain  it  at  a  permanently  greater  E.M.F.  than 
0"6  y^  salt  solution.  It  is  therefore  out  of  the  question  that 
the  antagonistic  effects  above  quoted  should  be  due  to  the  action 
of  the  water  of  liquefaction,  when  the  mucosa  is  cooled  by  the 
application  of  snow  or  ice.  Such  solutions  as  contain  salt  enough 
to  cause  dehydration,  to  a  greater  or  less  degree,  of  the  tissues  in 
contact  with  them,  produce  a  reverse  effect  from  water  or  highly 
dilute  salt  solution.  With  such  we  always  find  (e.g.  with  0*8- 
1"5  ^  NaCl  solution)  a  comparatively  rapid  fall  of  E.M.F. 
in  the  ingoing  tongue  current,  which,  between  certain  limits, 
rises  again  with  equal  rapidity  when  water  is  added. 

It  is  very  remarkable  that  in  this  case  also,  as  on  ener- 
getic cooling  of  the  tongue,  there  may  be  a  true  reversal  of  the 
normal  ingoing  current,  although  the  strength  of  the  opposite 
current  is  generally  far  behind  that  produced  by  the  action  of 
cooling.  It  is  possible  in  the  same  preparation,  by  alternate 
immersion  in  1  ^  and  2  ^  salt  solution,  to  give  a  success- 
ively incoming  and  outgoing  direction  to  the  current  many 
times  over.  As  a  rule,  a  few  minutes  are  sufficient  to  initiate 
these  changes.  Engelmann  had  already  found  in  the  frog's  skin 
that  very  low  differences  in  concentration  of  the  salt  solutions 
produced  extraordinary  alterations  in  electromotive  response, 
from  which  we  may  conclude  a  singular  sensibility  of  the  aative 
elements  concerned,  with  regard  to  changes  in  the  water  content. 
It  is  well  known  that  even  while  the  frog's  tissues  are  living, 
water  may  be  drawn  out  of  them  vigorously  by  injecting  strong 
solutions  of  common  salt  or  glycerin  at  the  back  of  the  head. 
Half  a  cc.  of  the  latter  injected  into  the  dorsal  lymph-sac  of  a 
curarised  frog  is  sufficient  in  a  short  time  (1  —  2  hours)  to  draw 


V      ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      473 

off  SO  much  water  from  the  watery  tissues  of  the  tongue,  tliat 
they  appear  visibly  shrunken  and  darker  in  colour  than  under 
normal  conditions.  In  this  state  the  entering  current  of  the 
mucosa  is  always  very  weak  or  wholly  wanting. 

These  last  appearances  lead  directly  to  the  consideration  of 
the  mode  of  action  of  other  substances  which  produce  chemical 
metabolism  in  the  living  cell.  In  the  first  place  there  are  the 
two  gases  which  play  such  an  important  part  in  the  vital  processes 
of  the  organism,  oxygen  and  carbon  dioxide,  whose  special  signi- 
ficance for  certain  electromotive  reactions  of  plants  and  animals 
is  well  established.  Engelmann  showed  that  on  dri^dng  out 
oxygen  by  an  indifferent  gas  (N  or  H)  the  E.M.F.  of  the  skin 
current  sinks  gradually,  increasing  again  quickly  so  soon  as 
atmospheric  air  is  reintroduced,  until  the  initial  height  is  not 
only  reached,  but  even  exceeded.  C0„,  on  the  other  hand,  pro- 
duces an  extremely  rapid  fall  of  E.M.F.,  which  is  only  arrested 
when  the  surrounding  atmosphere  contains  a  low  percentage  of 
the  gas.  A  similar  effect  of  want  of  0  has  been  recently 
demonstrated  in  plant  currents  by  Haacke  {Flora,  1892,  Heft 
iv.)  We  can  attest  a  similar  effect  of  these  two  gases  upon  the 
frog's  tongue.  The  method  of  experiment  was  essentially  based 
upon  that  of  Engelmann ;  the  preparation  (lower  jaw  and  tongue 
lying  on  a  block  of  salt  clay)  was  placed  with  the  leading-off 
electrodes  in  a  gas-chamber,  consisting  of  a  glass  vessel,  with  four 
tubes,  through  which  the  gases  could  be  led  into  the  chamber. 
The  E.M.F.  of  the  incoming  lingual  current  invariably  fell  on 
driving  out  0,  as  well  as  on  introducing  COg,  in  the  first 
case  rather  slowly,  in  the  second,  on  the  contrary,  very  rapidly. 
This  simple  contrivance  may  also  be  employed  for  testing  anccs- 
thetics  (ether,  chloroform) :  even  a  small  quantity  of  these  sub- 
stances in  the  form  of  vapour  produces  a  considerable  diminution 
of  E.M.F.  in  the  entering  current,  which,  if  the  action  does  not 
last  too  long,  is  restored  by  driving  pure  air  through  the 
chamber. 

The  mucosa  of  the  throat  and  cloaca  of  the  frog  give  precisely 
similar  relations.  Engelmann  (77)  had  previously  demonstrated 
electromotive  effects  in  both  these  preparations.  Again,  in  both 
cases,  we  have,  under  normal  conditions,  an  "  entering "  current, 
often  of  considerable  E.M.F.,  and  hardly  below  that  of  the  lingual 
current.     Yet  the  histological  structure  is  widely  different.     Both 


474  ELECTRO-PHYSIOLOGY 


in  throat  and  cloaca  the  mucous  coat  is  "  glandless "  in  the 
ordinary  acceptance  of  the  word,  there  being  in  both  cases  only 
a  single  layer  of  cylindrical  epithelium,  consisting  in  the  throat 
of  ciliated  cells  with  goblet  cells  interspersed  between  them,  in 
the  cloaca  almost  exclusively  of  the  latter.  Multicellular  glands 
are  entirely  wanting.  From  these  very  reasons  the  preparations 
afford  much  more  obvious  and  simple  conditions  of  leading-off 
than  the  lingual  mucosa,  so  that  certain  objections  to  which  the 
latter  is  fairly  liable  drop  out  of  court  without  prejudice.  Since 
in  the  cloacal  mucosa  ciliated  cells  are  altogether  wanting,  while 
its  electromotive  action  corresponds  in  every  respect,  on  the  one 
hand  with  that  of  the  ciliated  mucosa  of  the  throat,  on  the  other 
with  the  sparsely  ciliated  lingual  mucosa,  we  cannot  but  conclude 
that  in  all  three  cases  the  true  electromotive  elements  are  the  mucous 
cells,  luhether  present  as  elements  of  compound  glands,  or  as  gohlet 
cells.  But  it  was  necessary  to  test  this  view,  inasmuch  as  Engel- 
mann  held  the  ciliated  cells  themselves  to  be  the  active  electro- 
motive elements,  and  was  inclined  to  derive  the  throat  current 
from  them.  Hermann,  too,  indicated  as  a  possibility  that  the 
ciliary  movement  might  be  regarded  "  from  the  point  of  view  of 
an  ('  irritative ')  alteration  occurring  in  the  external  cell-layers." 
Our  own  observations  do  not,  however,  bear  out  this  suggestion. 

The  method  of  investigation  both  in  throat  and  cloaca  was 
extremely  simple.  Engelmann,  as  a  rule,  separated  out  the 
mucosa  from  the  layers  beneath  it,  and  led  off  from  the  inner 
and  outer  surfaces  of  the  membrane  stretched  over  a  cork. 
But  even  with  the  greatest  precautions  this  entails  some 
mechanical  injury,  and  since — as  we  have  frequently  experienced 
— the  intensity  of  electromotive  action  in  the  mucosa  is  affected 
to  an  extraordinary  degree  by  even  the  slightest  stretching 
or  tearing,  it  is  preferable  to  lead  off  from  the  mucosa  in 
situ.  For  this  it  is  only  necessary  to  remove  the  outer  skin 
of  the  head  as  far  as  the  wall  of  the  upper  jaw,  so  as  to  avoid 
any  accidental  interference  from  its  electromotive  properties,  and 
then  to  cut  out  the  whole  upper  jaw  by  as  deep  a  section  as 
possible.  This  is  placed  in  a  watch-glass  in  a  little  0*5  ^ 
salt  solution,  with  the  mucous  surface  uppermost,  after  which  it 
is  only  necessary  to  dip  one  brush-electrode  into  the  latter,  while 
the  point  of  the  other  is  in  contact  with  any  point  of  the  mucous 
surface,  in  order  to  lead  off  with  as  little  disturbance  as  possible. 


V      ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      475 

Under  these  conditions  the  entering  current  is  much  stronger 
than  in  the  separated  membrane,  and  the  only  doubt  can  be 
whether  electromotive  action  of  other  parts  (injured  muscles, 
etc.)  may  not  be  involved  in  it.  Such  interference  can  easily  be 
excluded  if  the  same  preparation  is  examined,  as  before,  after 
destruction  of  the  surface  epithelium,  or  the  entire  removal  of  the 
ciliated  mucosa.  We  have  never  then  observed  any  marked 
differences  of  potential,  so  that  this  objection  must  be  regarded  as 
unfounded.  The  mucous  coat  of  the  cloaca  is  usually  examined 
hj  slitting  the  cloaca  longitudinally  as  cautiously  as  possible,  and 
spreading  it  out  on  a  clay  block  without  actually  touching  the 
mucous  surface,  which  can  then  be  led  off  as  usual. 

Up  to  a  certain  point  the  mere  look  of  the  membrane  will 
show  in  the  one  case,  as  in  the  other,  whether  it  will  yield  a 
strong  or  weak  current.  If  the  mucosa  of  the  throat  (as  is  usual 
in  winter)  looks  transparently  pink  and  moist,  and  if  the  cloaca 
is  filled  with  soft  or  liquid  matter,  a  strong  current  may  be 
reckoned  on  with  tolerable  certainty  ;  but  if,  on  the  contrary  (as 
is  usual  in  summer  with  frogs  that  have  been  in  hand  a  long- 
time), the  ciliated  mucosa  is  dim  and  pale,  or  the  cloaca  contains 
only  a  few  hard  excreta,  the  entering  current,  although  generally 
present,  will  be  extremely  feeble.  This  seems  a  direct  indication 
that  the  secretory  activity  stands  in  both  cases  in  immediate  and 
close  relation  to  the  electromotive  action  of  the  mucous  membrane. 
To  this  it  must  be  added  that  the  ciliary  movement  often 
occurs  normally,  as  far  as  may  be  judged  from  the  onward  move- 
ment of  blood  platelets  or  similar  bodies,  while  the  entering 
current  is  quite,  or  almost,  wanting ;  and  we  have,  on  the  other 
hand,  though  more  rarely,  observed  cases  in  which,  notwithstand- 
ing a  weak  ciliary  motion,  the  E.M.F.  of  the  current  was  unusually 
high.  The  mucosa  in  this  case  was  invariably  covered  with 
a  tolerably  thick  layer  of  slimy  secretion.  It  would  appear 
that  the  mechanical  injuries  associated  with  exposure  and 
extension  have  a  much  less  pernicious  effect  upon  the  ciliary 
movements  of  the  mucosa  of  the  throat  than  upon  its  electro- 
motive action.  We  have  frequently  observed  in  these  prepara- 
tions that  the  ciliary  motion  continues  for  hours  with  the  utmost 
vivacity,  while  minimal  deflections  alone  indicate  the  presence  of 
a  weak  entering  current.  The  effects  of  pilocarpin  poisoning  may 
also  be  quoted  in  favour  of  the  view  here  advanced,  which  regards 


476  ELECTRO-PHYSIOLOGY 


the  entering  "  rest  current "  of  the  throat  mucosa  as  a  "  secretion 
current."  The  lingual  current  is  usually  found  at  a  certain 
stage  of  pilocarpin  poisoning  (two  hours  after  injection  of 
1  cc.  of  2  y^  solution  of  pilocarp.  muriat.)  to  be  extremely 
vigorous,  and  the  same  is  true,  according  to  our  experiences,  of 
the  throat  and  cloacal  currents.  The  deflection  is  normally  so 
strong  that  the  scale  flies  off  the  field. 

Since  there  appears  from  the  above  experiments  to  be  no  pro- 
portion between  vigour  of  ciliary  movements  and  intensity  of 
electromotive  action,  while  the  observations  of  Engelmann,  which 
seem  to  indicate  such  a  relation,  are  capable  of  quite  another  in- 
terpretation, we  have  so  far  failed  to  discover  any  reason  why  the 
entering  current  of  the  mucosa  should  be  referred  to  any  other 
cause  than  the  homodromous  lingual  or  cloacal  currents,  unless  in 
the  sequel  there  proves  to  be  similar  electromotive  action  on 
the  part  of  a  membrane  consisting  only  of  ciliated  cells.  We 
have  seen  that  the  uniformity  of  electromotive  reaction  in 
the  two  preparations  in  question,  and  the  lingual  mucosa,  is 
almost  perfect.  This  is  true  not  only  of  the  inconstancy  of  the 
current,  but  also  of  the  effects  of  cooling  and  excitation.  In 
nearly  every  case  in  which  the  E.M.F.  has  reached  a  certain 
height,  oscillations  of  the  magnet  may  be  observed,  from  which 
we  may  conclude  the  presence  of  heterodromous  forces,  the  sum 
of  which  corresponds  with  the  momentary  deflection.  And 
just  as  this  magnitude  alters  with  time  at  one  and  the  same 
point,  it  may  vary  at  different  points  of  the  mucosa  at  the  same 
moment.  As  a  rule  the  entering  current  of  the  cloacal  mucosa 
is  far  more  vigorous  than  that  of  the  throat — as  might  be 
expected  a  priori  if  the  unicellular  glands  (goblet  cells)  are  to 
be  held  responsible  for  it. 

Engelmann  had  observed  that  this  current  is  weakened  by 
cooling,  but  it  escaped  his  notice  that  under  uniform  conditions 
a  total  reversal  may  be  possible.  In  fact,  nothing  is  easier  than 
to  convince  oneself  that  by  laying  a  preparation  of  the  upper 
jaw  in  0'5  %  NaCl  solution  cooled  to  zero,  the  strongest 
entering  current  may  be  made  to  disappear  in  the  shortest  pos- 
sible time  (5  —  10  minutes).  Immersion  in  warmed  salt 
solution  (about  25-30°  C.)  calls  back  the  normal  current 
almost  instantaneously.  In  order  to  produce  an  "  outgoing " 
current  of  any  considerable  proportions,  it  is,  as  a  rule,  necessary 


V     ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS     477 

to  make  use  of  melted  snow  or  ice  ;  it  also  depends  conspicuously 
upon  certain  conditions  in  the  mucosa,  which  again  are  due  to 
environment  during  the  life  of  the  frog.  In  the  throat, 
as  in  the  tongue,  the  best  and  most  convincing  results  are 
obtained  when  the  preparation  is  taken  from  a  warm  frog,  and 
the  original  entering  current  not  too  pronounced.  Accord- 
ingly the  frogs  (B.  temporaria,  not  curarised)  intended  for  this 
experiment  were  usually  left  two  to  three  days  in  a  warm 
room  near  the  stove.  In  order,  as  far  as  possible,  to  avoid 
mechanical  excitation  of  the  mucosa  by  friction  or  pressure,  it 
was  found  best  to  apply  loose  melting  snow,  a  lump  of  which 
was  placed  upon  the  mucosa  of  the  skinned  upper  jaw,  and 
several  times  renewed  before  the  current  of  rest  was  tested. 
The  water  of  liquefaction  is  carefully  removed  with  a  brush,  and 
the  leading-off  electrodes  arranged  in  such  a  way  that  they  are 
divided  by  a  not  too  thick  layer  of  melting  snow  from  the  mucous 
surface  below  them.  Immediately  after  reading  the  scale  the 
galvanometer  is  opened  again  by  removing  the  electrodes  from 
the  mucosa,  so  as  to  avoid  the  development  of  accidental  "  thermo- 
currents  "  as  far  as  possible.  Exactly  the  same  method  is  employed 
to  investigate  the  effect  of  cold  upon  the  cloacal  current.  In 
the  one  case,  as  in  the  other,  a  very  rapid  fall  of  the  original 
E.M.F.  is  visible,  accompanied,  generally  speaking,  by  reversal  of 
the  current,  upon  which  it  often  reaches  such  proportions  that 
the  spot  flies  off  the  scale.  When  the  snow  is  entirely  melted  the 
original  E.M.F.  of  the  current  usually  comes  back  in  consequence 
of  the  increasing  temperature.  The  experiment  may  be  repeated 
many  times  on  the  same  preparation  with  identical  results. 

We  cannot  doubt  that  the  cooling  of  the  surface  epithelium 
here,  as  in  the  tongue,  leads  pe?^  se  to  the  appearance  of  hetero- 
dromous  electromotive  force. 

The  skin  of  the  leech  is  another  no  less  favourable  object  for 
the  study  of  electromotive  action  in  superficially  flattened,  uni- 
cellular, mucous  glands.  After  removing  the  connective  tissue 
it  is  easy  to  free  the  skin  with  scissors  from  all  ragged  ends  of 
tissue,  so  that  only  the  cuticular  muscle-layer  is  left.  Then, 
on  leading  off  from  external  and  internal  surface,  there  is  in- 
variably a  strong  entering  current,  which  reacts  under  different 
conditions  as  described  above. 

The   well-known   homodromous   electromotive   action   of  the 


478  ELECTRO-PHYSIOLOGY 


skin  in  lower  vertebrates  (amphibia  and  fishes)  must  be  referred 
essentially  to  the  same  causes  as  in  the  organs  previously 
described. 

By  far  the  most  thorough  investigations  relate  to  the  electro- 
motive action  of  the  external  skin  of  the  frog,  and  we  are  more 
especially  indebted  to  Engelmann  (72)  for  a  series  of  excellent 
observations,  the  value  of  which  is  in  no  way  lessened  by  the  in- 
correct interpretation  he  puts  upon  them.  More  recently,  starting 
from  certain  theoretical  considerations  given  above,  Hermann  has 
again  made  the  skin  of  the  fish  the  object  of  investigation,  with 
results  that  are  conclusive  as  regards  his  interpretation  of  the 
frog's  skin-current. 

Since  the  skin  of  certain  fishes  is,  in  those  points  which  seem 
most  essential  to  electromotive  activity,  precisely  similar  in 
construction  to  the  objects  last  under  discussion,  a  few  observa- 
tions upon  it  may  be  quoted,  i'rom  the  researches  of  F.  E. 
Schultze  (78),  it  has  long  been  known  that  there  is  a  varying 
mass  of  unicellular  mucous  glands,  in  the  form  of  goblet  cells,  in 
the  cuticle  of  many  fishes,  which  in  some  cases  compose  the 
whole  of  the  epithelium  (Cobitis).  The  individual  elements 
often  reach  a  considerable  size,  and  yield  a  mucous  secretion, 
which  makes  the  upper  skin  smooth  and  slimy.  As  always, 
the  protoplasmic,  nucleated  portion  of  the  cell  is  basal,  i.e. 
directed  towards  the  cutis,  while  the  upper  portion  engaged  in 
transforming  the  mucin  opens  directly  upon  the  free  surface  of 
the  upper  skin.  At  the  present  time  there  cannot  be  the 
slightest  doubt  as  to  the  secretory  function  of  these  cells,  since 
the  process  may  actually  be  watched  under  the  microscope. 
Hermann,  in  particular,  has  contributed  valuable  data  re 
electromotive  activity  of  the  skin  of  fishes.  As  compared  with 
frogs,  fish  are  less  suitable  objects,  inasmuch  as  their  upper  skin 
is  not,  as  in  the  frog,  separated  by  great  lymph  spaces  from  the 
muscle,  but  grows  into  it.  In  many,  and  indeed  most  cases 
therefore,  it  is  only  possible  to  test  the  P.D.  between  a  corroded 
point  of  skin  (i.e.  incapable  of  electromotive  action)  and  one 
that  is  normal,  when  there  will  usually  be  a  strong  current 
in  the  same  direction  as  in  the  frog's  skin  and  mucous  membranes 
{supra)  under  corresponding  conditions,  i.e.  the  corroded  point  of 
the  skin  is  "  energetically  positive  to  non-corroded  points." 

We  must,  with  Hermann,  conclude  from  this  fact  "that  the 


V      ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      479 

skin  of  the  fish,  or,  more  correctly,  every  spot  on  the  superficies 
of  tlie  fish,  is,  in  exactly  the  same  way  as  the  skin  of  the  frog, 
the  seat  of  an  electromotive  force  directed  from  without  inwards, 
and  very  easily  disturbed  by  corrosion."  In  the  eel  it  is  not 
difficult  to  strip  off  the  entire  skin,  or  to  prepare  pieces  of  it, 
but  it  is  advisable  in  all  cases  that  the  fish  under  examination 
should  be  as  fresh  and  uninjured  as  possible,  since  the  electro- 
motive activity  easily  receives  a  permanent  check  from  any  slight 
injury.  E.  Waymouth  Keid  and  Tolputt  (83)  have  recently 
observed  reversal  of  the  current  on  fatigued  animals. 

Under  normal  conditions  the  rest  current  of  the  frog's  skin 
agrees  perfectly  with  that  of  the  fish — save  from  its  greater 
strength  in  most  cases — although  the  histological  structure  of  the 
two  objects  presents  fundamental  differences.  Mucous  cells  are 
not,  as  with  the  fish,  the  chief  constituents  of  the  surface 
epithelium  proper,  but  are  confined  almost  exclusively  to  the 
multicellular  skin  glands  ;  the  epithelium,  on  the  other  hand,  is 
composed  almost  exclusively  of  polyangular  prickle  and  bristle 
cells,  those  next  to  the  cutis  being  more  cylindrical  in  shape, 
while  towards  the  surface  they  get  more  and  more  flattened,  and 
are  eventually  covered  over  with  a  single  layer  of  flattened  epi- 
thelium. Only  a  few  solitary  goblet  cells,  small  and  flask-shaped, 
are  found  in  the  epithelium,  near  the  surface,  and  even  these 
(according  to  F.  E.  Schultze)  do  not  open  upon  it. 

Engelmann's  observations  (as  confirmed  by  the  author) 
are  the  best  authority  in  regard  to  the  normal  entering  rest 
current  of  the  frog's  skin — which  is  mainly  to  be  referred  to 
the  great  number  of  skin  glands  present. 

The  dependence  of  E.M.F.  in  the  skin  current  upon  the 
bulk  of  water  in  the  tissues  is  once  more  apparent.  We 
can  readily  see  that  the  current  will  become  weaker,  in  pro- 
portion as  the  epidermis  gets  drier,  since  the  resistance  to  con- 
ductivity increases  enormously  with  the  latter.  Simple  moistening 
with  water  or  dilute  salt  solution  produces  a  rapid  and  consider- 
able increase  of  E.M.F.  in  each  such  case.  The  greatest  remainder 
of  E.M.F,  is  obtained  with  pure  water.  "  If  a  drop  of  salt  solu- 
tion of  0'2  ^  is  applied,  after  washing  with  water  has 
brought  the  E.M.F.  to  a  constant  height,  it  begins  to  decrease 
after  a  few  minutes.  Eepeated  dropping  of  the  same  solution 
depresses  it  still  further,  until  it  reaches  a  constant  level.      A 


480  ELECTRO-PHYSIOLOGY 


prolonged  water-bath  finally  raises  the  E.M.F.,  in  many  cases,  to 
the  same  height  as  before  the  application  of  the  salt  solution " 
(Engelmann).  Stronger  solutions  of  salt  (0'4  —  0"8  ^)  act 
still  more  strongly  and  energetically.  These  experiments  on 
the  extraordinary  effect  of  even  very  slight  changes  of  concentra- 
tion upon  the  magnitude  of  E.M.F.  in  the  skin  current  cannot 
obviously  be  referred  to  changes  of  conductivity,  but  undoubtedly 
depend  upon  variations  in  the  electromotive  functions  of  the 
active  cells,  which  go  hand  in  hand  with  changes  in  bulk  of 
water  in  the  same.  The  skin  of  the  frog  is  less  sensitive  than 
that  of  the  tongue  to  mechanical  impacts  (pressure,  traction). 
Still,  after  severe  traction  Engelmann  found  {I.e.)  that  the  E.M.F. 
fell  in  a  few  seconds  from  0"1  Dan.  to  0"006  Dan.  Protracted 
cold  caused  greater  or  less  diminution  of  the  entering  normal 
rest  current,  without,  however,  reversing  it.  At  a  temperature 
of  -1-4°  C.  Engelmann  still  observed  an  E.M.F.  of  0-08  Dan. 
Negative  variations  as  a  rule  correspond  with  sudden  positive 
heat  variations,  their  duration  and  magnitude  growing  with 
increasing  magnitude,  duration,  and  spatial  extension  of  the 
rise  of  temperature.  Among  chemical  agents  COg  is  emphatic- 
ally a  substance,  the  effect  of  which  is  to  diminish  the  force  of 
the  skin  current  "  with  extraordinary  rapidity."  In  the  space  of 
the  first  half  minute  Engelmann  has  often  seen  it  fall  to  a  sixth, 
and  less,  of  the  original  height.  If  the  poisonous  gas  is  removed 
soon  enough  (by  blowing  in  air  or  hydrogen)  the  E.M.F.  may 
return  to  its  original  proportions.  So  too,  though  in  different 
degrees,  the  action  of  ansesthetics  like  chloroform  and  ether, 
which  also  produce  marked  negative  variations  even  in  minimum 
doses. 

Want  of  oxygen,  too,  weakens  the  skin  current  after  a  long 
period,  and  may,  after  1  —  2  hours,  reduce  it  to  zero.  With 
renewal  of  air  the  E.M.F.  increases  more  rapidly  than  it  had 
previously  diminished,  provided  that  oxygen  had  not  been  drawn 
off  for  too  long  a  period. 

The  great  variability  of  skin  and  mucosa  currents,  and  their 
extreme  dependence  on  the  most  varying  external  influences, 
lead  us  a  priori  to  anticipate  that  the  effects  of  artificial  excita- 
tion (whether  direct  or  from  the  nerve)  would,  according  to 
circumstances,  differ  very  considerably.  Here  again  the  frog's 
tongue  affords  by  far  the  most  favourable  conditions  for  experi- 


V     ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      481 

ment,  since  the  nerves  that  supply  its  glands  can  be  exposed 
without  difficulty. 

We  have  seen  the  extent  to  which  the  strength  of  the  normal 
entering  "  tongue  current "  is  affected  by  the  least  disturbance  to 
the  surface  of  the  mucosa.  In  nearly  every  case  it  increases 
rapidly  after  contact  with  the  point  of  the  leading-off  electrode, 
both  in  the  excised  tongue  and  in  the  preparation  in  situ. 
That  this  is  merely  due  to  the  decline  of  a  negative  variation 
(produced  by  contact  of  the  mechanical  stimulus)  in  the  current 
of  rest  follows  from  the  fact  that,  on  closing  the  galvanometer 
circuit,  the  slightest  movement  of  the  electrode  point  on  the 
surface  of  the  tongue,  or  gentle  rubbing  of  the  spot  led  off, 
at  once  produces  a  rapid  fall  of  E.M.F.,  which  usually  occurs 
the  more  vigorously  in  proportion  with  the  strength  of  the 
maximal  rest  current.  This  negative  variation  declines  very 
rapidly,  and  may  often  be  reproduced  if  the  excitation  is  repeated. 
Experiments  to  determine  the  magnitude  of  excitation  required, 
show  that  extremely  slight  impacts  are  needed  under  favourable 
conditions.  Stroking  with  the  point  of  a  hair,  or  the  fall  of  a 
drop  of  salt  solution,  nearly  always  produces  a  marked  variation. 
With  stronger  excitation  distributed  over  a  larger  area,  the  effect 
is  increased,  and  a  current  of  rest  that  is  not  too  strong  may 
easily  be  reversed  under  these  conditions,  especially  if  (e.g. 
through  moderate  cooling)  there  is  an  a  jJriori  tendency  in  that 
direction.  If  kept  at  a  low  temperature  in  a  little  water,  weakly 
curarised,  B.  temjjoraria  will  often  exhibit  a  reversed  (outgoing) 
rest  current  of  considerable  dimensions,  if  the  leading-off  elec- 
trodes are  placed,  one  on  the  surface  of  the  tongue,  the  other  on 
the  exposed  muscles  of  the  leg,  directly  after  the  lower  jaw  has 
been  drawn  back  by  a  thread  previously  passed  through  it. 
This  outgoing  current,  which  must  certainly  be  referred  in  part 
to  cooling,  is  often  as  strong  as  the  normal  entering  current,  but 
diminishes  rapidly  if  the  electrodes  are  left  undisturbed,  and  finally 
becomes  reversed,  i.e.  normal.  During  the  whole  of  this  period 
the  slightest  friction  with  the  tip  of  the  electrode  in  contact 
with  the  tongue  will  at  once  produce  a  swing  back  of  the 
magnet,  in  the  direction  of  increase  of  the  outgoing,  or  diminution 
of  the  incoming,  current,  followed  again  by  a  prompt  reversal. 
In  such  cases  the  reversed  current  immediately  after  the  throat 
has  been  opened  is  doubtless  only  partially  due  to  the  previous 

2  I 


482  ELECTRO-PHYSIOLOGY 


cooling,  and  far  more  to  the  unavoidable  mechanical  excitation  of 
the  mucosa  on  freeing  the  tongue  from  the  palate,  to  which  it 
adheres  in  the  natural  position. 

The  normal  entering  current  also  declines  considerably  under 
similar  conditions,  and  apparently  from  the  same  reason,  and  may 
even  be  abolished.  If  the  same  point  of  the  lingual  mucosa, 
which  at  first  reacts  strongly  (in  the  direction  of  decline  of 
negativity)  when  gently  rubbed  with  the  tip  of  the  electrode,  is 
repeatedly  excited  in  the  same  way,  the  negative  variation  grows 
weaker  at  each  excitation,  and  at  last  there  will  be  no  reaction ; 
the  normal  current  of  rest  is  unaltered  in  strength,  notwith- 
standing the  excitation.  The  E.M.F.  of  the  latter  sometimes 
appears  to  increase  considerably  in  consequence  of  temporary, 
local,  mechanical  excitation ;  but  the  method  employed  is 
hardly  suited  to  the  solution  of  this  and  other  questions,  and  it 
is  advisable  to  employ  some  stimulus  that  can  be  better  graduated 
as  regards  intensity  and  duration.  The  electrical  current  in  the 
form  of  the  tetanising  alternating  currents  of  an  induction  coil 
is  the  best  fitted  for  this  purpose. 

If  the  secondary  coil  is  connected  with  two  electrodes  of 
platinum  wire,  which  are  then  brought  into  contact,  at  a  distance 
of  3  —  5  mm.,  with  the  moist  surface  of  a  block  of  salt  clay  (as 
used  for  testing  the  tongue  current), — while  the  one  brush  electrode 
is  in  leadino'-off  contact  with  the  lateral  surface,  the  other  with 
the  upper  surface  of  the  block,  between  the  two  platinum  wires, — 
no  trace  of  deflection  will  be  detected  in  the  galvanometer  in  the 
circuit,  if  the  circuit  of  the  secondary  coil  is  closed  by  Wagner's 
vibrating  hammer,  and  the  coil  not  pushed  home ;  but  even  in 
the  latter  case  there  are,  as  a  rule,  only  very  weak  effects  on  the 
galvanometer,  which  in  no  way  modify  the  consequences  of  ex- 
citation to  be  described  hereafter.  Before  testing  these  on  the 
living  tongue,  we  ascertained  of  course  by  repeated  experiments 
that  the  results  described  with  the  clay  block  underwent  no 
alteration  when  a  dead  lingual  preparation,  incapable  of  yielding 
electromotive  action,  was  placed  upon  it. 

If,  on  the  other  hand,  such  excitation  experiments  are  tried 
on  normal  tongue  preparations — set  up  and  led  off  as  above — 
enormously  marked  effects  may  sometimes  be  seen,  and  almost 
exclusively  in  the  direction  of  a  negative  variation  of  the  rest 
current.      Here  again  we  see  to  a  striking  extent  the  dependence 


V      ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      483 

of  the  magnitude  of  excitation  effect  upon  the  strength  of  the 
current  of  rest,  as  expressed  both  in  the  degree  of  deflection  with 
a  given  intensity  of  excitation,  and  in  the  fact  that  it  takes  less 
strength  of  coil  to  produce  a  given  deflection  in  proportion  as  the 
E.M.F.  of  the  current  of  rest  is  lower.  When  the  last  is  at  a 
considerable  height  we  have  often,  after  compensating  —  with 
the  coil  at  160  (1  Dan.  in  the  primary  circuit) — observed  a 
negative  variation  which  drove  the  scale  far  off  the  field  of  vision. 
At  the  same  time  the  changes  of  form  and  position  in  the  tongue 
in  consequence  of  direct  muscular  excitation  were  so  insignificant 
as  to  exclude  the  possibility  that  the  effects  described  can  be 
caused  by,  or  along  with,  them.  Still  it  cannot  be  denied  that 
these  accessory  effects,  which  are  inevitable  with  strong  currents, 
do  produce  a  most  undesirable  complication,  and  we  have  there- 
fore endeavoured  to  determine  by  special  control  experiments  to 
what  degree  the  excitation  effects  observed  on  the  galvanometer 
are  actually  affected  by  them.  It  is  not  difficult  to  abolish  the 
electromotive  activity  of  the  lingual  mucosa,  either  locally  at  the 
lead-off,  or  on  the  entire  surface,  without  affecting  the  deeper 
muscles,  and  with  these  the  mobility  of  the  tongue.  If  the 
appearance  of  the  negative  variation  has  been  ascertained  at  any 
given  position  of  the  coil,  and  a  grain  of  salt  is  then  applied  to 
the  tip  of  the  lingual  electrode,  there  will  follow  immediately 
(partly  in  consequence  of  chemical  excitation)  a  very  rapid  and 
marked  diminution  of  force  in  the  entering  rest  current.  The 
excitation  previously  employed  will  now  be  ineffective,  although 
the  lingual  muscles  contract  after  as  before  stimulation.  The 
same  result  is  obtained  on  cautiously  treating  the  mucosa  with 
ISTHg  in  gas  or  solution.  So  that,  while  there  can  be  no 
doubt  that  we  have  to  include  the  mechanical  excitation  due 
to  movements  of  the  tongue  contracting  under  the  leading-off 
electrodes,  it  may,  on  the  other  hand,  be  accepted  that  the 
main  result  in  this  case  is  due  to  the  electrical  excitation  of  the 
mucosa.  As  a  proof  of  this  we  may  instance  the  behaviour  of 
small  fragments  of  the  mucous  coat,  which  are  easily  separated 
with  scissors  from  the  subjacent  muscle-layer.  As  was  said 
above,  these,  when  examined  on  clay,  as  a  rule  exhibit  before 
long  a  vigorous  current,  which  on  tetanising  yields  a  strong 
negative  variation  without  any  material  change  of  form  in  the 
fragment. 


484  ELECTRO-PHYSIOLOGY  chap. 

The  behaviour  of  the  cooled  lingual  mucosa,  giving  opposite 
electromotive  action,  is  of  interest ;  here,  too,  there  is  normally  a 
negative  variation,  i.e.  diminution  of  E.M.F.  in  the  outgoing 
current,  but  this  effect  is  generally  much  less,  and  therefore 
demands  much  stronger  currents,  than  in  the  normal  incoming 
rest  currents.  While  this  is  the  usual  result  with  weak  alternating 
currents,  approximation  of  the  coil  under  otherwise  uniform  con- 
ditions will  often  cause  a  positive  variation  after  a  first  negative 
swing  of  greater  or  less  amplitude,  i.e.  a  temporary  increase  of  the 
outgoing  current  occurring  in  the  return  process. 

As  regards,  finally,  the  time-relations  of  the  variation,  these, 
with  an  entering  current  of  rest,  are  highly  characteristic. 
Without  employing  any  finer  artificial  means,  a  latent  period 
("  stage  of  latent  electromotive  action,"  Engelmann)  may  invari- 
ably be  determined,  its  duration  being  essentially  conditioned  by 
the  strength  of  excitation,  in  the  sense  that  it  decreases  inversely 
with  increasing  strength  of  current.  The  deflection  begins 
slowly  at  first,  and  rapidly  attains  its  full  value  later ;  as  a  rule, 
the  return  swing  of  the  magnet  begins  while  the  excitation  is  still 
in  progress,  and  if  the  secondary  circuit  is  left  closed,  runs  in  a 
zigzag  course,  sometimes  interrupted  by  short  backward  move- 
ments in  the  direction  of  the  negative  variation.  If,  on  the 
contrary,  the  excitation  ends  as  soon  as  the  deflection  has  reached 
its  maximum,  there  will  always  be  a  rapid  and  uniform  return 
swing  of  the  magnet,  during  which  the  E.M.F.  of  the  current  not 
only  regains  its  original  proportions,  but  nearly  always  exceeds 
them  to  a  marked  extent,  so  that  we  are  justified  in  saying  that  the 
negative  variation  further  entails  a  weaker  positive  variation,  which 
is  relatively  slower  in  its  development,  and  still  more  in  its  decline. 
If  a  sufficiently  long  interval  is  allowed  between  each  pair  of 
excitations,  the  experiments  may  be  repeated  with  uniform  results. 
Sometimes,  however,  the  amplitude  of  the  negative  variation 
suddenly  diminishes,  and  with  each  excitation  there  is  a  negative 
after-effect,  which  finally  causes  a  permanent  diminution  of  E.M.F. 
in  the  current.  It  is  also  important  to  avoid  too  rapid  fatigue  of 
the  preparation,  by  an  undue  length  of  each  individual  excitation  ; 
protracted  tetanus  soon  weakens  the  entering  current  perma- 
nently. We  have  already  shown  that  the  negative  variation  of  the 
ingoing  rest  current  is  in  a  marked  degree  dependent  on  the 
strength  of  the  latter,  and  diminishes  very  rapidly  with  the  fall 


V      ELECTROMOTIVE  ACTIOIST  OF  EPITHELIAL  AND  GLAND  CELLS      485 

of  its  E.M.F.  This  is  best  examined  in  preparations  where 
normal  electromotive  activity  has  previously  been  altered  in 
various  degrees  by  treatment  with  dehydrating  salt  solutions.  It 
is  then  found  without  exception  that  the  negative  variation  is  less 
on  direct  excitation  of  the  lingual  mucosa,  in  proportion  with  the 
weakness  of  the  entering  current.  Soon,  however,  another  pheno- 
menon makes  its  appearance  in  the  gradual  development  of  a 
positive  fore-swing  and  positive  after-effect,  which,  as  it  were, 
enclose  the  negative  variation.  Sometimes  the  latter  is  wholly 
wanting,  and  even  with  strong  excitation  there  will  be  only  a 
monophasic,  positive  deflection,  often  of  considerable  dimensions. 
This  only  occurs,  however,  at  a  very  advanced  stage  of  dehydration. 
Having  in  view  the  facts  communicated  above,  which  refer 
exclusively  to  the  results  of  direct  excitation  of  the  lingual 
mucosa,  we  may  curtail  the  discussion  of  the  following,  i.e.  the 
appearances  due  to  indirect  excitation  from  the  nerve,  since  in  all 
essential  points  they  coincide  with  the  former.  Hermann  and 
Luchsinger  (79),  examining  into  the  "secretion  currents"  of  the 
frog's  tongue  when  led  off  from  two  symmetrical  points  on  the 
mucosa  with  excitation  of  the  glossopharyngeal  or  hypoglossal 
nerve,  express  the  "  perfectly  regular  "  result  of  their  experiments 
as  follows :  "  After  a  visible  latent  period,  the  excitation  of  a 
glossopharyngeal  nerve  produces  a  current  in  the  excited  mucosa, 
— ingoing  at  first,  but  which  immediately  gives  way  to  an  outgoing 
direction, — after  which  there  is  once  more,  whether  the  excitation 
is  over  or  in  progress,  a  powerful  incoming  current  that  long 
outlasts  the  excitation  (where  this  is  not  continued),  reaching  its 
maximum  slowly,  and  then  disappearing  again  with  extreme 
reluctance."  This  effect  will  be  seen  to  agree,  generally  speaking, 
with  the  results  of  direct  excitation  experiments,  apart  from  the 
positive  fore-swing  and  (in  our  observations  far  less  strongly 
marked)  positive  after-effect  of  the  second  negative  phase,  which 
we  have  only  observed,  in  the  manner  described  by  Hermann,  in 
preparations  where  the  normal  electromotive  activity  is  already 
considerably  weakened.  Our  own  experiments  relate  throughout 
to  specimens  of  R.  towporaria  kept  over  winter  during  the  months 
of  January  and  February.  We  held  it  advisable  with  regard  to 
the  comparison  possible  between  the  series  of  experiments  described 
above,  and  those  to  be  discussed  in  the  sequel,  to  continue  leading 
off  from  the  upper  and  lower  surface  of  tlie  tongue,  with  com- 


486  ELECTRO-PHYSIOLOGY  chap. 

pensation  of  the  strong  entering  current  which  under  these  con- 
ditions is  almost  invariably  present.  The  frog  was  usually 
slightly  curarised — to  the  point  of  immobility — immediately 
before  the  experiment,  since  it  seemed  probable  that  the  effects  of 
excitation  would  be  seriously  weakened  if  the  poisoning  had 
occurred  longer  before,  even  if  the  circulation  was  normal,  and 
the  heart  vigorously  beating.  In  agreement  with  Hermann  and 
Luchsinger,  we  found  that  the  glossopharyngeal  nerve  acted 
like  the  hypoglossal,  and  there  was  at  most  a  difference  of 
degree  in  favour  of  the  former.  Since  this  is  much  more 
quickly  and  conveniently  prepared,  the  following  experiments  are 
almost  wholly  based  upon  it.  In  normal,  powerfully  developed, 
entering  rest  currents,  we  invariably  found  as  the  effect  of 
excitation  of  the  nerve  a  monophasic,  negative  variation,  the 
magnitude  of  which  is  dependent,  as  we  have  seen,  on  the  force  of 
the  compensating  current ;  this  makes  itself  evident  a  short 
time  (1-3  sees.)  after  the  beginning  of  the  excitation,  and  often 
reaches  very  considerable  proportions.  We  never,  however, 
observed  reversal  of  a  strong  normal  current  in  consequence  of 
excitation.  As  a  rule,  after  long  protracted  excitation  of  the 
nerve,  the  return  swing  of  the  magnet  begins  while  it  is  still  in 
progress,  and  oscillations  are  again  to  be  observed  frequently,  the 
back  swing  being  interrupted  by  renewed  impacts  in  the  direction 
of  the  negative  variation.  If  the  exciting  circuit  is  opened  at 
the  moment  when  the  magnet  is  on  the  point  of  turning,  or  a 
little  earlier,  the  development  of  the  original  current  follows 
more  quickly  than  when  the  excitation  is  continuous ;  it  is  also 
evident  that  the  backward  phase  of  the  negative  variation 
follows  regularly  with  increasing  rapidity ;  and  it  is  equally  the 
rule  that  the  original  current  of  rest  is  strengthened  by  excita- 
tion, as  was  stated  by  Hermann.  In  our  experiments,  however, 
this  positive  "  after -variation "  was  never  stronger  than,  or 
even  approximately  as  strong  as,  the  preceding  negative  variation. 
Under  normal  conditions  we  have  only  seen  this  last  introductory 
positive  phase  on  a  few  occasions,  and  can  therefore  as  little 
attribute  to  it,  as  to  the  positive  after- variation,  the  significance 
attached  to  it  by  Hermann ;  according  to  our  experiences  the 
negative  variation  of  the  incoming  current  of  rest  has  far  more 
the  appearance  in  every  case  of  the  undoubtedly  characteristic 
effect  of  excitation,  while  the  positive  effect  on  the  other  hand 


V      ELECTEOMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      487 

always  retreats  into  the  background.  Yet  this  is  by  no 
means  to  say  that  the  contrary  might  not  occur  under  other 
conditions.  The  preceding  statement  refers  only  to  lingual 
preparations  which  exhibit  the  normal  reaction,  i.e.  vigorous 
entering  mucosa  current.  It  is  also  quite  indifferent  in  what 
manner  the  lead-off  is  effected.  In  the  entire  uninjured  frog 
we  have  either  led  off  from  the  muscles  of  the  leg  and  upper 
lingual  surface,  or  made  use  of  the  previously  described  prepara- 
tion of  the  lower  jaw,  which  is  easily  brought  into  connection 
with  the  glossopharyngeal  nerve,  so  that  the  experiments  in 
question  are  directly  comparable  with  the  former.  The  last- 
named  experiments  made  it  possible  to  test  the  excitation  of  the 
nerve  on  preparations  of  the  tongue  in  which  the  entering  rest 
current  has  been  weakened,  or  reversed,  by  treatment  with 
strong  (0'8-l"5  %)  NaCl  solution.  As  the  nerve  is  not  in- 
jured by  a  short  application  of  solutions  of  this  concentration, 
the  excitation  effects  (manifestations)  observed  must  principally 
be  referred  to  the  changes  undoubtedly  present  in  the  glandular 
cells  excited.  In  such  cases  we  have  frequently  noted  excitation 
effects  which  correspond  throughout  with  those  described  by 
Hermann  and  Luchsinger,  a  strong  positive  effect  being  periodically 
interrupted  by  a  weaker  negative. 

There  is  accordingly  complete  agreement  in  nearly  every 
point  of  electromotive  action  between  direct  and  indirect  excitation 
of  the  lingual  mucosa,  another  proof  that  in  the  methods  of  direct 
excitation  employed  we  are  only  deahng  with  effects  which 
originate  in  the  mucosa.  Another  question,  on  the  other  hand,  which 
cannot  be  answered  as  certainly,  is  whether  in  the  previous  instances 
direct  and  indirect  excitation  must  not  be  regarded  as  identical,  in 
so  far  as  only  the  nerves  which  are  situated  in  the  mucosa  are 
excited  in  the  first  case  also.  Some  poison  is  required  which,  like 
curare  in  striated  muscle,  will  entirely  abolish  nerve  action  with- 
out injuring  the  gland  cells.  Atropin  at  once  suggests  itself, 
as  having  long  been  known  to  abolish  the  effect  of  excitation  in 
secretory  nerves  completely  and  permanently,  in  the  most  different 
glands.  Hermann  and  Luchsinger  showed  that  it  had  the  same 
effect  on  the  galvanic  effects  of  excitation  in  the  frog's  tongue. 
Both  after  direct  dropping  on  to  the  tongue,  and  subcutaneous 
injection,  the  strongest  excitation  of  the  nerve  is  ineffective, 
although,  as   we   have   repeatedly   ascertained,  direct   excitation 


ELECTRO-PHYSIOLOGY 


of  the  mucosa  after,  as  well  as  before,  continues  to  produce  a 
strong  negative  variation  in  the  existing  rest  current.  After  large 
doses  and  longer  poisoning  we  frequently  found  not  merely  that 
the  incoming  current  of  rest  was  considerably  weakened,  but  that 
the  results  of  direct  electrical  excitation  were  reduced  in  a  marked 
degree.  The  conclusion  is  that  atropin  principally  paralyses  the 
gland  nerves,  without  seriously  injuring  the  cells. 

It  may  be  taken  as  proved  that  not  only  the  glands  of  the 
external  skin,  but  nearly  all  the  glandular  organs,  are  essentially 
affected  by  pilocarpin,  as  regards  their  state  of  activity,  in  the 
sense  of  a  long-protracted,  energetic  excitation.  Having  ourselves 
(80)  thoroughly  investigated  the  action  of  pilocarpin  poisoning  upon 
the  morphological  behaviour  of  the  lingual  glands  in  the  frog,  it 
was  the  more  interesting  to  determine  the  concomitant  galvanic 
phenomena.  In  experiments  many  times  repeated,  in  which 
the  (non-curarised)  frogs  were  injected  with  1  cc.  of  2  ^ 
solution  of  pilocarp.  muriat.  under  the  skin  of  the  back,  we 
invariably  found  two  hours  afterwards  that  the  entering  mucosa 
current  of  the  tongue  (which  was  covered  with  a  visible  layer  of 
secretion)  was  developed  with  unusual  vigour,  and  was  often  of 
considerable  proportions.  Corresponding  with  this,  the  negative 
variation,  both  with  direct  and  indirect  excitation,  was  extremely 
pronounced,  and  nothing  has  come  under  our  notice  so  well 
calculated  to  exhibit  the  above-described  normal  reaction  of  the 
tongue  in  excessive  proportion,  as  pilocarpin  poisoning. 

With  regard  to  the  action  of  this  drug  it  was  to  be  expected 
a  jJriori  that  a  long -protracted  excitation  of  the  secretory 
nerves  would  produce  a  similar  effect.  As  in  the  salivary 
glands,  so  too  in  the  mucous  glands  of  the  frog's  tongue,  it  is 
possible  by  introducing  a  metronome  into  the  circuit  of  the 
secondary  coil  to  extend  the  excitation  of  the  corresponding 
secretory  nerves  over  several  hours,  without  fear  of  too  rapid  ex- 
haustion of  the  glands.  Deep-seated  histological  changes  ensue 
in  both  cases,  which  are  in  close  relation  with  the  secretory 
process  (80). 

If,  during  such  rhythmical  persistent  excitation,  the  electro- 
motive phenomena  are  observed  in  the  tongue  (which  should 
preferably  be  in  situ,  with  intact  circulation),  there  will  be  found 
without  exception  after  a  longer  or  shorter  period — during  which 
the  initial  current  appears  weakened  in  consequence  of  the  pre- 


V      ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      489 

dominance  of  the  opposite  current  (negative  variation) — a  gradual, 
and,  for  the  most  part,  irregular  augmentation  of  the  original 
ingoing  current,  which  obviously  corresponds  with  the  positive 
after-effect  of  a  short  excitation,  and  may  sometimes  attain 
important  dimensions.  But  the  mucosa  current,  even  after  long- 
protracted  excitation,  will  always  continue  to  be  directed  inwards. 
The  mucosa  of  the  throat  and  cloaca  are  of  course  capable 
of  direct  electrical  or  mechanical  excitation  also,  and  the  effects 
are  essentially  the  same  as  in  the  tongue,  although  these  tissues 
are  as  a  rule  less  sensitive.  While,  as  we  have  seen  above,  the 
slightest  contact  with  the  lingual  mucosa  produces  a  negative 
variation  of  the  normal  entering  current,  which  rapidly  declines 
again  as  soon  as  the  excitation  is  over,  this  is  by  no  means 
usual  in  the  throat  or  cloacal  mucosa.  In  these  a  comparatively 
strong  pressure,  or  pull,  is  required  to  produce  any  considerable 
depression  of  the  "  rest  current,"  which  subsequently  proceeds 
as  in  the  tongue.  Much  better  results,  and  the  only  ones  that 
are  adapted  to  exact  investigation,  are  yielded  by  local  tetanising 
with  the  induction  current.  As  regards  the  method  employed, 
we  may  refer  throughout  to  what  has  already  been  cited.  In 
a  preparation  of  the  throat  mucosa  with  very  strong  entering 
currents,  excitation  with  gradual  approximation  of  the  coil 
produces  even  with  weak  currents  (coil  at  180)  a  distinct 
monophasic  negative  variation  of  the  compensated  rest  current, 
which  increases  rapidly  as  the  coil  is  pushed  up,  although  even 
in  the  most  favourable  cases  it  does  not  go  so  far  that — as  is 
usual  in  the  tongue  under  similar  conditions — the  scale  flies 
off  the  field.  A  slight  tremor  at  the  beginning  of  the  deflection 
sometimes  betra,ys  the  existence  of  a  heterodromous  force,  which, 
as  we  shall  see,  leads  under  other  conditions  to  a  ijositive  varia- 
tion. If  the  excitation  is  interrupted  before  the  scale  has  come 
wholly  to  rest,  the  return  swing  of  the  magnet  begins  rapidly 
at  first,  and  then  travels  more  slowly  to  its  zero,  sometimes  even 
beyond,  in  the  sense  of  a  reinforcement  of  the  original  current 
(positive  after-effect).  The  manifestation  of  excitation  is  quite 
altered  when  the  E.M.F.  of  the  entering  current  of  rest  is 
lower.  As  in  the  tongue,  only  perhaps  still  more  markedly, 
the  strength  of  the  negative  variation  depends  upon  the  initial 
intensity  of  the  normal,  electromotive  action  of  the  mucosa. 
If  this  sinks   below  a  certain  limit,  there   appears  regularly  in 


490  ELECTRO-PHYSIOLOGY 


place  of  the  monophasic,  negative  variation,  a  diphasic,  and 
with  very  weak  excitation,  a  monophasic,  positive  variation. 
The  excitation  effects  are  then  dissimilar  in  detail,  and  to  a 
certain  extent  very  complicated.  Generally  speaking,  it  may 
he  said  that  the  positive  variation  preponderates  the  more,  in 
proportion  as  the  exciting,  incoming  mucosa  current  is  ah  initio 
weaker,  while  on  the  other  hand  the  negative  effects  hecome 
more  and  more  prominent  with  increasing  strength  of  excita- 
tion, so  that  when  the  coil  is  pushed  nearly  home  there  will  in 
the  majority  of  cases  be  only,  or  at  any  rate  chiefly,  negative 
variation,  the  more  or  less  delayed  entrance  of  which  often 
indicates  the  concealed  presence  of  the  opposite  force.  So  too 
the  rapid  back  swing  of  the  magnet  to  its  position  of  rest  and 
even  beyond  it,  as  is  often  seen  with  lower  excitation  intensities ; 
the  primary,  at  first  ingoing,  negative  variation  always  exceeds 
the  subsequent  positive  swing  in  magnitude  in  such  a  case,  as 
shown  by  the  rapid  reversal  (when  the  exciting  circuit  is  closed) 
of  the  magnet  deflected  towards  the  negative  variation :  from 
this  there  is  but  a  step  to  the  reaction  in  which  the  proportions 
of  the  two  antagonistic  deflections  are  inverted,-  the  negative 
variation  appearing  only  as  a  short  prelude  to  the  subsequent 
positive  swing,  which  often  under  these  conditions  attains 
considerable  amplitude,  although  the  deflections  caused  by  it 
never  equal  those  of  the  stronger  negative  variation.  Finally 
(with  the  lowest  effective  intensity  of  excitation),  all  direct 
expression  of  the  negative  variation  may  be  wanting,  a  more  or 
less  definite  retardation  in  the  positive  deflection  being  the  sole 
indication  of  its  presence.  On  cooled  preparations,  where  the 
entering  current  was  at  zero,  we  have,  even  with  the  coil  pushed 
home,  obtained  only  simple,  positive  deflections  (in  the  direction 
of  the  original  E.M.F.  of  the  current),  and  of  no  considerable 
strength.  It  is  perfectly  easy  to  remove  the  objection  that  the 
excitation  effects  described  are  caused  by  fallacies  of  any  kind ; 
it  is  only  needful,  as  has  already  been  described  at  length,  to 
render  the  mucosa  incapable  of  electromotive  action,  or  to 
remove  it  entirely,  in  order  to  be  certain  that  even  on  applying 
strong  currents,  excitation  effects  are  totally  wanting. 

The  non-ciliated  cloacal  mucosa  and  the  skin  of  the  leech 
react  to  electrical  excitation  readily  like  the  ciliated  throat 
mucosa.      Here  again,  only  perhaps  in  a  still  higher  degree,  the 


V     ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      491 

influence  of  the  initial  force  of  the  incoming  current  upon  the 
excitation  effects  is  apparent.  The  threshold  of  excitation 
actually  lies,  as  a  rule,  much  higher  than  in  the  throat  mucosa. 
Before  there  is  any  definite  effect  in  one  or  the  other  direction, 
there  will  often  be  an  uneasy  oscillation  of  the  magnet,  giving 
the  impression  that  two  antagonistic  effects  are  in  conflict. 
With  weak  currents  the  deflection  of  the  positive  variation 
finally  preponderates,  while  with  very  closely  approximated,  or 
closed -up,  coils,  the  contrary  is  the  case  without  exception. 
A  short,  positive  fore-swing  is  often  to  be  seen,  after  which 
occurs  the  much  stronger  negative  variation.  At  the  end  of 
the  excitation  the  latter  nearly  always  declines  rapidly  and 
completely.  In  several  cases  in  which  the  entering  rest 
current  exhibited  an  unwonted  intensity,  there  were,  from 
the  weakest  effective  currents  to  the  strongest,  only  pure 
monophasic  negative  variations,  which  then  attained  proportions 
that  are  usually  seen  in  the  tongue  only,  under  similar 
conditions.  Thus,  in  one  case,  the  cloacal  mucosa  of  a  non- 
curarised  H.  temporaria,  stretched  over  a  cork  frame,  and  led  off 
from  both  surfaces,  exhibited  an  incoming  current  of  such 
amplitude  that  the  scale  flew  off;  after  compensation  there 
was,  even  with  the  coil  at  180,  a  distinct,  negative  variation  of 
several  degrees  of  the  scale,  and  with  the  coil  at  100  the 
scale  vanished  on  excitation.  Unlike  the  throat  mucosa,  the 
deflection,  apart  from  small  oscillations,  remained  tolerably 
constant  so  long  as  the  excitation  continued,  after  which  it 
declined  rapidly.  Where  the  cloacal  mucosa,  as  seems  always 
to  be  the  case  if  there  is  no  fluid  secretion,  is  currentless, 
or  weakly  active  in  an  ingoing  direction  only,  the  strongest 
tetanising  with  the  coil  pushed  home  produces  no  visible 
negative  variation ;  there  is  either  no  effect  or  at  most  a  weak 
deflection  in  the  sense  of  an  ingoing  current.  This  shows  that 
the  excitation  effects  depend  upon  the  mucosa  itself,  and  are 
not  caused  by  the  muscles  lying  beneath  it. 

In  the  richly  glandular  skin  of  Amphibia,  the  results  of 
direct  and  indirect  excitation  are  essentially  similar.  Engel- 
mann  {I.e.  p.  136)  carried  out  experiments  in  which  pieces  of 
skin  {B.  temporaria)  were  excited  by  single  make  or  break  shocks 
from  an  ordinary  induction  apparatus,  the  induction  currents 
being   led   in   by   the   leading -off  electrodes.       At   the   moment 


492  ELECTRO-PHYSIOLOGY 


of  excitation  the  galvanometer  was  shut  off,  and  it  was  ascer- 
tained that  the  induction  currents  had  not  left  the  electrodes  per- 
ceptibly polarised.  "  Each  excitation  manifested  itself  by  a  sharp 
decline  of  electromotive  force.  This  decline  is  not  only  relatively 
but  absolutely  greater,  in  proportion  with  the  approximation  of 
the  coils,  while  at  uniform  distance  of  the  coil  it  is  much  stronger 
at  the  break  than  at  the  make  shock.  After  the  first,  second, 
and  third  excitation  a  positive  variation  (in  a  special  case)  follows 
the  negative  variation ;  the  fourth  excitation,  however,  weakens 
the  E.M.F.  permanently,  to  a  considerable  degree,  and  the  last 
and  most  powerful  break  shock  depresses  it  almost  to  zero,  and 
leaves  it  weakened  to  about  half  the  original."  Our  own  obser- 
vations agree  in  the  main  with  these  conclusions,  when  pieces  of 
skin — from  any  part  of  the  body  indifferently — are  stretched  on  a 
clay  block,  tetanised,  and  led  off  simultaneously  with  the  excita- 
tion. If  the  frogs  used  {towporaria)  have  been  kept  in  a  cool 
room  free  from  frost,  in  vessels  with  a  little  water,  the  electro- 
motive action,  i.e.  entering  current,  v/ill  regularly  and  invariably 
be  very  powerful,  with,  as  in  the  former  cases,  a  corresponding 
monophasic  negative  variation,  which  appears  even  at  a  compara- 
tively low  strength  of  current,  beginning  after  a  latent  period  of 
1—2  sees.,  and  reaching  its  maximum  value  tolerably  quickly  ; 
while  as  after-effect  of  the  excitation  a  more  or  less  considerable 
reinforcement  of  the  original  current  of  rest  is  usually  visible, 
which  declines  slowly,  and  never  approximates  to  the  strength 
of  the  negative  variation. 

Direct  electrical  excitation  of  the  skin  of  the  eel's  snout,  which 
consists  only  of  goblet  cells,  exhibits,  according  to  Eeid  and 
Tolputt  (83),  a  similar  reaction  to  that  of  the  frog's  cloacal  mucosa, 
i.e.  with  weak  excitation  and  a  low  development  of  the  rest 
current,  there  was  a  positive,  with  stronger  excitation  a  negative, 
variation  of  the  entering  current,  which  was  always  very  per- 
sistent. In  the  rest  of  the  eel's  skin  there  are,  together  with  a 
less  number  of  mucous  cells,  other  kinds  of  secretory  elements 
(club  cells),  which  seem,  as  regards  electromotive  response,  to  give 
an  opposite  reaction.  According  to  Eeid  and  Tolputt  (/.c),  there 
is,  with  a  strongly  developed  ingoing  current  and  strong  excitation, 
a  regular  increase  of  the  current  (positive  variation),  while,  con- 
versely, weak  excitation  and  low  intensity  of  the  existing  E.M.F. 
seem  to  favour  the  appearance  of  a  negative  variation. 


V      ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      493 

Our  experiments  show  that  the  results  obtained  with  indirect 
excitation  of  the  frog's  skin  from  the  nerve  agree  almost  exactly 
with  those  of  direct  excitation.  Eoeber  (I.e.  p.  3)  employed  a 
method  by  which  he  was  enabled  to  experiment  on  the  skin  of 
the  leg  without  much  injury  to  it,  and  this  is  to  be  preferred 
to  the  preparation  from  the  skin  of  the  back  used  later  on  by 
Hermann.  Under  all  conditions  it  involves  much  less  injury  to 
the  skin,  and,  apart  from  the  greater  resistance  of  the  prepara- 
tion, makes  it  easier  to  test  the  effect  of  different  reagents  on  the 
phenomena  of  excitation.  We  can  either  use  Eoeber's  original 
method,  in  which,  after  setting  up  an  ordinary  "  rheoscopic 
frog's  leg,"  the  skin  "  which  covers  the  whole  leg  up  to  the  knee- 
joint  is  divided  by  a  circular  cut  at  the  ankle  from  the  inferior 
portion,  spht  up  the  anterior  surface  by  a  longitudinal  cut,  and 
then  prepared  and  turned  back  from  the  entire  Hmb  ahnost  to 
the  knee-joint.  The  leg  is  then  divided  below  the  knee  and 
taken  off,  leaving  only  the  sciatic  nerve,  along  with  the  knee- 
,joint  and  skin  of  the  leg."  In  order  to  lead  off  the  skin  current 
the  prepared  flap  must  be  carefully  spread  out  on  a  clay  block, 
one  electrode  being  in  contact  with  this  latter,  the  other  with  the 
centre  of  the  exterior  skin  surface.  Hermann's  modification  (75), 
as  described  above,  is  yet  more  convenient  and  sparing  of  injury; 
the  whole  frog  is  used,  curarisecl  to  immobility,  when  the  current 
can  be  led  off  with  circulation  intact — after  freeing  the  pelvic 
portion  of  both  sciatics  (from  the  back) — either  from  symmetrical 
points  of  both  skinned  legs,  or,  as  is  perhaps  better,  from  some 
point  of  the  skin  of  the  leg,  and  the  exposed,  undisturbed  surface 
of  the  thigh  muscles  on  the  same  side.  In  the  latter  case  the 
whole  skin  current  comes  into  play,  and  must,  as  a  rule,  be  com- 
pensated beforehand. 

In  Eoeber's  experiment  it  was  found  that  where  the  entering 
skin  current  was  of  any  considerable  proportions,  excitation  of 
the  nerve  invariably  produced  a  greater  or  less  diminution  of 
E.M.E.,  and  "  as  this  occurs  in  a  preponderating  majority  of 
cases,"  Eoeber  does  not  consider  "  this  '  negative  variation ' 
of  the  gland  current  to  be,  generally  speaking,  the  consequence 
of  excitation  of  the  gland  nerves.  With  an  originally  low  magni- 
tude of  current,  on  the  contrary,  there  is  sometimes  increase 
instead  of  decrease,  a  positive  instead  of  a  negative  variation." 
Engelmann  also  found  in  the  same  object  an  almost  invariable 


494  ELECTRO-PHYSIOLOGY 


diminution  of  the  skin  current  in  consequence  of  nerve  excitation, 
whether  this  were  produced  electrically,  chemically,  or  mechanic- 
ally. Even  with  the  application  of  a  single,  vigorous,  make 
induction  shock  to  the  peripheral  stump  of  the  sciatic,  he  observed 
a  preliminary  fall  of  E.M.F.  to  25—30  %,  which  is  naturally 
even  more  considerable  with  tetanising  excitation.  Accord- 
ing to  Engelmann,  the  course  of  an  "  elementary  "  variation  in 
nerve  excitation  through  a  single  momentary  stimulus  is  as 
follows :  "  After  a  latent  period,  lasting  with  weak  excitation  for 
4  sees.,  with  stronger  excitation  for  less  than  |-  sec,  the  E.M.F. 
falls  at  first  with  increasing,  and  later  with  diminishing,  rapidity 
— reaching  its  minimum  after  a  few  seconds  with  weak  excitation, 
in  1 0-2  0  sees,  with  stronger  stimuli ;  it  rises  again  imme- 
diately, at  first  with  increasing  and  subsequently  with  diminishing 
rapidity,  eventually  reaching  its  original  proportions."  "  But  it 
does  not  often  remain,  stationary  at  this  point,  especially  when 
the  skin  has  been  resting  for  a  long  time  before  excitation.  More 
frequently,  during  the  next  few  minutes  it  rises  higher  in  propor- 
tion with  the  strength  of  the  previous  excitation  "  (positive  after- 
variation),  "  sinking  down  again  slowly  afterwards.  If  the  excita- 
tion is  repeated  frequently,  the  positive  after-variation  fails  to 
appear,  and  there  will  each  time  be  a  negative  variation  only. 
With  prolonged  tetanising  excitation  of  the  nerve,  the  depression 
of  E.M.F.  continues  much  longer,  and  outlasts  the  excitation. 
If  the  excitation  is  subsequently  very  vigorous,  the  positive  after- 
variation  may  be  wanting,  even  where  it  appeared  unmistakably 
after  a  short  excitation.  The  E.M.F.  then  remains  permanently 
depressed,  and  renewed  excitation  only  produces  an  insignificant 
diminution  of  it." 

Hermann  (82),  on  the  contrary,  finds  in  the  skin  of  the  lower 
limb,  and  more  particularly  in  the  skin  of  the  frog's  back,  in  con- 
sequence of  nerve  excitation,  either  a  2nire  iMsitive  variation,  or  the 
same  preceded  by  a  lugative  fore-swing,  "  which,  however,  is  usually 
much  weaker  than  the  positive  variation  itself  " — the  latter  being 
"  the  true  main  effect."  Hermann  only  found  a  pure  negative 
variation  twice  in  the  skin  of  the  back,  and  in  the  leg  "in  a 
negligible  number  of  cases  only "  (three  out  of  eighty  frogs). 
The  order  of  the  deflection  (in  skin  of  back  with  tetanising  ex- 
citation) is,  according  to  Hermann,  as  follows  :  "  At  first  the  scale 
remains  at  rest  for  several  (2-4)  sees. ;  after  this  latent  period 


V      ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      495 

a  tolerably  rapid  deflection  (in  the  positive  direction)  is  developed, 
but  remains  for  the  most  part  stationary,  after  which  a  slow 
■  further  growth  continues  to  the  maximum.  If  the  excitation  is 
protracted,  there  will  usually  be  reversal,  and  slow  return ;  if 
interrupted  at  the  height  of  its  deflection,  the  scale  will  remain 
at  the  point  of  deflection  for  some  time  longer,  or  else  continues 
its  course  a  little  further,  returning  then  more  slowly  than  the 
variation,  to  its  original  position."  Hermann  observed  the  same 
positive  deflection  after  very  short  excitation :  "  At  the  end  of 
such  excitation  the  scale  remains  at  rest  for  a  certain  time,  and 
then  pursues  its  deflection  in  the  positive  direction,  though  the 
variation  is  much  less  than  with  sustained  excitation."  Thus 
there  is  a  complete  antithesis  between  Hermann's  results  and  the 
earlier  conclusions,  which  is  but  little  modified  by  the  more 
frequent  appearance  of  a  "  negative  fore-swing "  on  the  skin  of 
the  lower  limb.  Both  Eoeber  and  Engelmann  have  observed 
pure  positive  effects  of  excitation  on  the  preparation  last  men- 
tioned, although  quite  exceptionally  and  under  conditions  in 
which  it  is  questionable  whether  the  phenomenon  is  to  be  re- 
garded as  "  normal."  This  was  the  case,  e.g.,  where  the  prepara- 
tion, after  being  uncovered  for  some  time  in  a  moist  chamber, 
exhibited  "  excessively  weak  "  (entering)  currents,  and  soon 
ceased  to  be  excitable.  Later  on  Bach  and  Oehler  (81)  found 
under  Hermann's  direction,  in  the  first  jjlace,  that  the  negative 
variation  of  the  entering  rest  current  of  the  skin  was  entirely 
dependent  upon  the  strength  of  the  latter  (a  fact  to  which  we 
have  frequently  referred  above),  and  on  the  other  hand  that  in  all 
cases  where,  whether  through  warming  beyond  a  certain  limit, 
or  painting  the  skin  with  strong  salt  solution,  the  "  current  of 
rest "  was  perceptibly  weakened,  its  negative  variation  declined 
rapidly,  finally  giving  way  to  "  an  incoming  secretion  current," 
i.e.  a  positive  variation.  From  this  we  may  assume  that  in 
Hermann's  experiments,  frogs  were  used  in  which  the  skin  current 
was  very  little  developed.  In  the  meantime  he  has  made  recent 
experiments  (82),  showing  that  in  certain  cases  there  is,  even 
with  a  strongly  developed,  entering,  rest  current  a  mainly  or 
exclusively  positive  variation,  when  the  nerves  of  the  skin  are 
excited.  This  may  be  demonstrated  on  the  skin  of  the  leg  in  the 
tree  frog,  as  well  as  on  the  skin  of  the  salamander  {Proteus 
anguineus). 


496  ELECTRO-PHYSIOLOGY 


If  every  diminution  of  the  normal  ingoing  skin  current  is 
thus  favourable  to  the  appearance  of  homodromous  (positive)  ex- 
citation effects,  it  is  a  /priori  possible  that  even  where  the  "  current 
of  rest "  is  altogether  wanting,  "  an  outgoing  secretion  current  " 
may  be  present.  In  fact,  Bach  and  Oehler  showed  that  whereas 
after  quite  a  short  (6—8  sees.)  action  of  saturated  solution  of  sub- 
limate the  skin  betrayed  hardly  any  electrical  activity,  excitation 
from  the  nerve  still  produced  tolerably  pronounced  effects,  always 
in  the  direction  of  an  entering  current.  We  cannot  agree  with 
Hermann  when  he  finds  in  this  fact  a  convincing  proof  that  the 
epithelial  layer  alone  is  intrinsically  the  seat  of  electromotive 
activity  in  the  unexcited  skin,  only  those  effects  which  occur  with 
nerve-excitation  ("  secretion  currents  ")  being  true  gland  functions. 
For  apart  from  the  fact  that  even  from  the  histological  point  of 
view  this  theory  is  highly  improbable,  it  is  also  quite  conceivable 
that  in  spite  of  the  short  duration  of  the  sublimate  bath,  traces 
of  the  substance  may  penetrate  into  the  gland  cells,  and  reduce 
their  normal  electromotive  activity,  i.e.  entering  current,  almost 
to  zero,  without  abolishing  it  completely.  We  have,  however, 
found  ample  proof  in  the  preceding  discussion,  that  under 
circumstances  in  which  any  kind  of  injury  has  weakened  the 
entering  current  of  the  mucous  secreting  cells  to  a  greater  or 
less  degree,  homodromous  effects  may  appear  with  direct  or  in- 
direct excitation. 

Since,  as  shown  by  Engelmann,  the  degree  of  moisture  in  the 
skin  is  far  the  most  important  factor  in  determining  the  strength 
of  its  normal  electrical  activity,  as  is  also  the  case  in  true  mucosse, 
we  should  a  priori  presume  that  it  would  be  possible,  by  altering 
the  bulk  of  water,  to  alter  the  direction  of  the  galvanic  effects 
occurring  when  the  skin  is  excited  as  in  the  foregoing.  Indeed 
the  experiments  on  the  mucous  coat  of  the  tongue,  throat,  and 
cloaca,  described  above,  points  in  this  direction. 

It  is  well  known  that  frogs,  when  kept  dry,  gradually  lose  a 
large  amount  of  water  through  the  skin,  but  it  would  take  a  long 
time  before  they  were  sufficiently  dehydrated  by  this  method  to 
be  fit  for  experiment.  This  is  effected  much  more  quickly  with 
the  aid  of  dehydrating  substances.  A  quantity  of  water  can  be 
drawn  out  of  the  frog's  tissues  in  the  shortest  possible  time  by 
the  simple  injection  of  strong  salt  solution,  or  glycerin  of  sufficient 
density,  under  the  skin  of  the  back. 


V     ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      497 

The  two  methods  may  be  combined  as  follows.  The  frogs, 
when  well  dried,  were  placed  in  a  large  open  glass,  with  a  wire 
cover,  the  sides  and  bottom  being  wrapped  in  a  clean,  dry  cloth. 
They  were  left  thus  in  a  warm  chamber  for  at  least  24  hours. 
They  were  next  curarised  as  slightly  as  possible  to  produce 
immobility,  and  when  paralysed,  1—2  cc.  of  .3—5  ^  salt 
solution,  or  better,  0"5— 1  cc.  glycerin,  were  injected  into  the 
dorsal  lymph  sac.  After  two,  at  most  three,  hours  the  dehydra- 
tion is,  as  a  rule,  sufficiently  advanced  for  the  experiments  to  be 
started.  It  is  unnecessary  to  enter  into  all  the  effects  which  can 
be  observed  on  these  frogs ;  they  are  sufficiently  well  known,  and 
have  no  immediate  connection  with  the  facts  before  us. 

If  the  electrical  activity  of  the  skin  of  such  "  dehydrated  " 
frogs  is  tested  as  usual,  either  on  single  excised  portions,  or  on 
the  entire  uninjured  animal,  the  insignificant  proportions,  or 
almost  complete  absence,  of  the  entering  current  is  very  striking. 
This  is  not  merely  due  to  the  greater  resistance  of  the  dry  skin, 
for  the  E.M.F.  is  slow  to  recover,  even  when  the  led-off  parts  of 
the  skin  are  freely  moistened  with  water  or  dilute  salt  solution. 
If  an  excised  portion  of  the  skin,  no  matter  from  what  part  of  the 
body,  is  now  excited  directly,  or  if  the  freed  sciatic  is  excited  by 
leading  off  from  the  external  surface  of  the  skin  of  the  leg,  and  the 
exposed  surface  of  the  muscles  of  the  thigh  on  the  same  side, 
there  will  under  all  circumstances  be  an  entering;  current,  i.e.  a 
positive  variation  of  the  current  of  rest,  which  either  makes  its 
appearance  alone,  or  is  introduced  by  a  short  negative  fore-swing. 
Under  these  conditions  there  is  never,  as  before,  a  mono-  . 
phasic  negative  effect.  As  regards  the  strength  of  the  positive 
effect  (always  in  the  direction  of  an  entering  rest  current), 
the  right  degree  of  dehydration  is  all-important,  and  there  is  a 
good  deal  of  uncertainty  in  obtaining  this.  In  favourable  cases 
the  positive  variation  may  become  as  marked  as  was  formerly  the 
strongest  negative  variation.  We  have  repeatedly  seen  deflections 
which  drive  the  scale  out  of  sight  when  the  current  of  rest  has  been 
compensated.  But  if  the  latter  is  still  considerable  the  positive 
variation  grows  less  and  less,  and  the  negative  fore -swing  is 
correspondingly  greater.  Sometimes  the  entering  skin  current  of 
the  leg,  immediately  after  freeing  the  sciatic  nerve  from  the 
pelvis,  is  extraordinarily  marked,  notwithstanding  the  previous 
dehydration,  and  this  is  usually  followed   by  a  tolerably  rapid 

2  K 


ELECTRO-PHYSIOLOGY 


diminution  during  the  experiment.  It  is  not  improbable  that 
this  is  due  to  a  (positive)  after-effect  of  excitation  of  the 
nerve,  produced  by  constriction.  In  such  a  case  it  is  best 
to  let  the  variation  decline,  and  then  excite  electrically.  In  this 
way  much  more  distinct  positive  variations  are  exhibited. 

The  order  of  the  deflections  produced  by  these  latter  is  almost 
invariably  such  that  after  the  expiry  of  the  latent  period  and 
eventually  of  the  negative  fore-swing,  the  positive  variation  is 
rapidly  initiated,  and  then  becomes  gradually  slower,  as  if  an 
antagonistic  effect  were  asserting  itself;  sometimes  it  continues 
only  for  quite  a  short  time,  or  even  swings  back  a  little,  in  the 
sense  of  a  negative  variation — finally,  however,  if  the  excitation 
is  prolonged,  the  positive  effect  breaks  through  again,  and  the 
deflection  becomes  more  characteristic.  We  are  of  opinion  that 
this  retardation  in  the  course  of  the  positive  variation  is  actually 
to  be  referred  to  the  opposite  action  of  a  simultaneously  excited 
negative  variation,  so  that,  as  always,  the  visible  deflection  is 
really  the  resultant  of  two  antagonistic  components.  It  is 
determined  by  the  preponderance  of  one  or  the  other  of  these 
forces. 

To  this  we  must  also  refer  the  fact  that,  at  a  certain  stage  of 
dehydration — which  is  safe  to  appear  when  the  frog  is  dried 
simply  by  long  detention  in  a  dry  chamber  without  water — the 
excitation  of  the  sciatic,  on  leading  off  from  the  skin  of  the  leg, 
which  usually  gives  a  strong  ingoing  current  only,  generally 
produces  a  distinct  and  fairly  vigorous  negative  variation  at  the 
first  excitation,  followed  by  a  weaker  positive  effect.  On  repeating 
the  excitation  at  a  later  stage,  no  definite  effect  is  usually 
apparent  ;  but  a  slight  swinging  to  and  fro  of  the  magnet,  or 
oscillation  at  its  zero,  indicates  an  interference  of  antagonistic 
forces,  which  are  nearly  balanced.  Under  these  conditions,  a 
complicated  variation  may  result  from  tetanising,  which  consists 
of  four  phases — an  initial  negative  deflection,  soon  interrupted  by 
an  essentially  stronger  positive  phase,  which  again  swings  back 
in  a  negative  variation,  and  finally  the  magnet  is  again  slowly 
reversed  in  the  direction  of  a  positive  swing.  The  whole  of  this 
complicated  process  occurs  during  the  excitation.  The  best  way 
to  observe  the  order  of  the  separate  phases  is  to  take  a  frog  at 
the  stage  of  dehydration  in  which  the  skin  of- the  leg  still  gives 
a  marked  ingoing  current,  and  each  excitation  is  accompanied 


V     ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      499 

by  a  plain  negative  variation,  followed  by  a  weaker,  positive 
swing — bleed  it,  and  expose  the  nerves — letting  it  then  lie 
in  the  chamber,  and  occasionally  testing  the  effects  of  ex- 
citation ;  the  ingoing  skin  current  then  declines  gradually,  the 
negative  variation  grows  weaker,  the  positive  effect  stronger,  and 
at  last  (after  a  brief  interval  of  total  failure  of  effect)  it  takes 
complete  possession. 

As  Hermann  pointed  out,  there  is  always  a  fairly  protracted 
after-effect  from  the  positive,  in  contradistinction  to  the  negative, 
variation^the  deflection  increasing  for  some  time  after  the 
excitation  is  over ;  the  decline,  too,  follows  more  slowly  than 
with  the  negative  variation. 

An  interesting  reaction  appears  in  frogs  (temporaria),  fresh 
caught  in  the  latter  half  of  February.  Any  point  of  the  skin 
at  fii'st  gives  a  vigorous  electrical  variation,  often  far  beyond 
the  scale ;  excitation  of  the  sciatic  produces  a  corresponding 
and  monophasic  negative  variation  in  the  skin  of  the  leg ;  this 
only  declines  very  gradually  and  incompletely,  so  that  a  strong- 
persistent  diminution  of  the  original  current  results,  which 
again  disappears  almost  entirely  after  a  second  short  excitation. 
A  third  experiment  is  followed  by  a  positive  effect,  preceded  by 
a  short,  negative  fore-swing.  In  another  frog  of  the  same  group, 
the  first  excitation  produced  such  a  marked  diminution  of  the 
original  ingoing  skin  current  that  even  at  the  second  excitation 
the  negative  was  replaced  by  a  positive  variation.  Here  we  have 
proof  of  the  extent  to  which  the  character  of  the  variation  is 
conditioned  by  the  strength  of  the  rest  current.  And  we  also 
learn  from  these  experiments  that  Engelmann's  attempted  ex- 
planation of  the  positive  effect  is  fallacious.  He  supposes  that 
the  positive  increment  produced  by  the  free  tension  at  the 
surface  of  the  epidermis,  in  consequence  of  surface  moisture  from 
the  skin  glands  emptied  during  excitation,  over-compensates  the 
negative  effect  originating  in  the  decline  of  glandular  energy. — 
This  theory  assumes  that  the  surface  cell-layers  form  a  compara- 
tively non-conducting  layer  in  consequence  of  dehydration,  "  only 
a  small  fraction  of  the  electrical  tensions  derived  from  glandular 
activity  being  apparent  at  its  surface."  Yet  such  could  not  be 
the  case,  either  in  the  instances  quoted  above,  or  in  the  dehy- 
drated frogs.  For  iii  the  first  case,  no  water  had  been  drawn  off, 
and  the  vigorous  primary  skin  current  shows  that  the  glands  were 


500  ELECTRO-PHYSIOLOGY 


ab  initio  concerned  in  its  production.  In  the  second,  no  trace  of 
secretion  even  with  the  magnifying  lens  was  to  be  discovered 
during  excitation  of  the  dry  surface  of  the  skin,  whicli  is  so  easy 
to  detect  under  normal  circumstances.  The  result  remained  the 
same  when  the  skin  surface  was  moistened  with  water,  or 
0'5  y^  salt  solution.  Hermann  subsequently  applied  the  same 
process  of  secretion  to  the  interpretation  of  the  contrary  effect — 
the  negative  variation  —  in  the  entering  skin  and  lingual  rest 
current  (frog).  He  starts  with  the  assumption  that  the  skin 
glands  are  normally  "  nearly  closed  to  the  external  surface,  i.e. 
have  no  external  galvanic  relation."  If  during  excitation  a 
sudden  compression  of  the  liquid  contents  sets  up  a  deflection  of 
the  ingoing  current  in  the  glandular  epithelium,  then — under  the 
further  presumption  of  a  homodromous,  electromotive  activity  of 
the  remaining  epithelium  — "  the  relation  of  E.M.F.  between 
glandular  skin  and  epithelium  "  determines  the  character  of  the 
phenomena  of  excitation. 

If  the  first  is  greater,  a  positive  increment  of  the  rest  current 
appears,  an  "  ingoing  secretion  current."  "  If  the  E.M.F.  of 
the  gland  epithelium,  on  the  contrary,  is  less  than  that  of  the 
skin  epithelium,  as  must  be  presumed  in  the  resting  state  of  the 
glands,  the  mere  mechanical  process  of  secretion  will  produce  a 
diminution  of  the  rest  current,  followed  however  by  augmentation, 
so  soon  as  the  excitation  of  the  nerve  incites  the  cells  to 
secretory  activity."  Notwithstanding  Hermann's  recent  protest 
(82),  we  continue  to  hold  this  explanation  fallacious,  and  are  still 
of  opinion  that  the  conditions  of  leading  off  are  similar  to  those 
in  the  frog's  tongue. 

The  electromotive  action  of  the  mucosa  of  the  stomach  claims 
attention  both  on  theoretical  grounds,  and  in  regard  to  the 
disputed  question  as  to  the  existence  of  special  secretory  nerves 
to  the  glands.  We  found  above,  as  first  stated  by  Eosenthal  (*73), 
that  the  mucous  coat  of  the  frog's  stomach  had  normally  the 
same  electromotive  action  as  the  outer  skin  of  fishes  and  naked 
amphibia,  i.e.  on  leading  off  from  the  free  internal  surface  and 
muscular  coat  a  powerful  ingoing  current  is  exhibited,  which 
Eosenthal  does  not  hesitate  to  connect  with  the  mucous  glands. 
Yet  in  view  of  the  facts  discussed  above  we  must  admit  another 
possibility,  viz.  that  the  whole  surface  epithelium  may  consist  of 
elements,  which  are  to  be  regarded  as  unicellular  mucous  glands 


V      ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS  .    501 

in  the  same  sense  as  the  goblet  cells  of  throat  or  cloacal  mucosa,  or 
the  gland  cells  of  the  frog's  tongue.  These  being  incontestably 
electrically  active,  we  may  affirm  with  almost  positive  certainty 
that — granting  the  glands  of  the  stomach  proper  to  possess 
electrical  action — the  ingoing  mucous  current  must  consist  of  at 
least  two  components. 

In  order  to  decide  this  question,  F.  Bohlen  (84)  carried  out 
under  our  direction  a  series  of  experiments  (on  the  frog  in  the  first 
instance),  the  object  of  which  was  to  demonstrate  the  influence  of 
the  digestive  activities  of  the  stomach  upon  its  electromotive 
properties.  If  these  really  depended  on  the  gastric  glands,  we 
should  expect  to  find  considerable  alterations  in  the  fasting  state, 
vs.  state  of  digestion.  This  proved  to  be  the  case,  but  not,  as 
was  expected,  in  the  sense  of  augmentation  of  the  "  current  of 
rest "  in  the  replete  animal,  but  on  the  contrary  of  a  marked 
diminution.  Only  when  indigestible  substances,  such  as  stones, 
wood,  etc.,  which  excite  the  mucosa  meclianically,  were  introduced 
into  the  stomach,  an  often  considerable  increase  of  the  normal, 
ingoing  current  became  perceptible,  together  with  increase  of 
mucous  secretion.  This  was  to  a  marked  degree  the  case  after 
the  introduction  of  bismuth  subnitrate,  where  the  sharp-edged 
crystals  seemed  to  act  as  an  intense  stimulus,  and  produced  a 
quite  specific  mucous  secretion.  When  the  insoluble  salt  reaches 
the  cloaca,  it  causes  a  marked  secretion  of  mucin,  and  a  corre- 
sponding augmentation  of  the  electrical  current,  so  that — as  in 
the  stomach — the  scale  flies  beyond  the  field  of  vision.  For 
the  rest,  the  E.M.F.  of  the  mucosa  of  the  stomach  is  con- 
ditioned, as  in  other  secreting  membranes  referred  to  (which 
secrete  mucin  only),  by  a  variety  of  factors :  in  particular, 
temperature,  dehydration  and  turgor,  anaesthesia,  etc.  Direct 
electrical  excitation  by  rapidly  alternating  shocks  from  an  in- 
duction coil  effects  at  a  small  distance  of  coil  a  negative  variation, 
usually  preceded  by  a  positive  swing.  The  strength  of  the 
original  current  is  therefore  of  essential  significance,  since  the 
deflection  corresponding  with  the  negative  variation  is,  so  to 
speak,  in  direct  ratio  with  the  E.M.F.  of  the  preparation. 

In  warm-blooded  animals  also  (rabbit,  guinea-pig,  rat)  Bohlen 
ascertained  the  existence  of  a  vigorous  ingoing  current.  After 
opening  the  belly,  an  unpolarisable  tube  electrode  closed  with  a 
clay   stopper   was   passed   through   a   hole  in   the   wall   of    the 


502  ELECTRO-PHYSIOLOGY  chap. 

stomach,  the  other  bemg  in  contact  with  the  external  surface  of 
the  stomach.  This  in  rabbits  and  guinea-pigs  is  nearly  always 
crammed  with  food,  so  that  the  lead-off  from  the  mucosa  is  here 
complicated  by  the  contents  of  the  stomach,  which  suggests  cer- 
tain objections.  In  the  first  place,  one  asks  whether  warmth 
may  not  have  a  perceptible  effect  on  the  electrode  inserted  deep 
into  the  stomach ;  in  the  second,  differences  of  potential  are 
caused  by  the  contents  of  the  stomach,  so  that  the  results  of  the 
observation  are  disturbed  to  an  extent  which  it  is  impossible  to 
calculate. 

In  regard  to  the  first  question,  it  is  easy  to  see  that  the 
currents  caused  by  differences  of  temperature  do  not  come  into 
the  reckoning  at  all,  in  comparison  with  the  marked  effects  of  the 
physiological  mucosa  current.  The  second  question  is  solved  by 
the  fact  that  almost  directly  after  the  death  of  the  animal  there 
is  a  decline  of  E.M.F.  which  soon  tends  to  reversal  of  the 
current,  but  this  current  appears  in  the  same  way  and  at  the 
same  intensity  whether  the  stomach  is  emptied  and  washed,  and 
then  led  off  directly  from  the  surface  of  the  mucosa,  or  whether 
it  is  already  empty,  e.g.  in  rats  that  have  been  kept  without  food 
for  some  days. 

In  warm-blooded  animals,  as  in  the  frog,  the  intensity  of  the 
rest  current  varies  in  individual  cases,  within  a  certain  range. 
Sometimes,  nearly  always  indeed,  it  is  so  strong  that  the  scale 
flies  far  off  the  field ;  in  other  cases  again  only  deflections  of  a 
few  degrees  are  visible.  Oscillations  occur  almost  invariably, 
which  are  of  very  different  magnitudes. 

The  effect  of  deep  narcosis  upon  the  strength  of  the  current 
in  the  mucosa  of  the  stomach  is  very  striking  in  mammals. 
With  a  little  care  in  the  use  of  chloroform  and  ether,  the 
variation  can  be  diminished  until  the  deflection  barely  reaches 
10  degrees  of  the  scale.  A  long  period  must  then  elapse  before 
the  current  returns  to  its  original  magnitude.  Whether  this 
is  a  direct  or  indirect  effect  is  foreign  to  our  present  discussion. 

As  in  the  frog,  so  in  warm-blooded  animals,  the  E.M.F.  of 
the  mucosa  is  considerably  heightened  by  the  introduction  of 
bismuth  (2—5  grs.  in  emulsion),  along  with  which  there  is 
an  easily-confirmed  increase  in  the  mucin  secretion. 

Artificial  excitation  of  the  vagus  nerve  produces  striking 
consequences.     While  the  only  result  in  the  frog  is  a  weak,  positive 


V     ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      503 

variation  of  the  entering  current,  which  appears  whether  the 
stomach  is  excised  or  in  situ, — in  mammals,  after  a  transitory 
increase  of  the  entering  current,  there  regularly  appears  a  negative 
variation  which  can  reach  such  proportions  that  the  current  not 
only  sinks  to  zero,  but  goes  beyond  it  in  the  reversed  direction, 
so  that  the  now  outgoing  current  may,  under  certain  conditions, 
become  as  strong  as  the  original  ingoing  current.  That  this  is 
not,  as  might  have  been  supposed,  an  action  of  secretory  nerves, 
but  merely  an  after-manifestation  of  the  disturbance  of  the  cir- 
culation due  to  the  slowing  or  stand-still  of  the  heart,  and,  in  the 
first  degree,  to  the  marked  fall  of  hlood-pressure,  is  very  easily 
determined.  It  appears  not  merely  from  the  time  coincidence  of 
the  latter  and  the  negative  variation,  but  more  particularly  from 
the  fact  that  whatever  depresses  blood -pressure  locally  or  in 
general,  also  tends  to  diminish  the  ingoing  current  of  the  stomach. 
This  applies  to  every  severe  loss  of  blood,  and  notably  still  more 
where  clamping  of  the  aorta  has  temporarily  produced  a  complete 
aucBmia  of  the  stomach.  The  current  diminishes  almost  at  the 
moment  when  anaemia  sets  in,  just  as  with  vagus  excitation,  to 
recover  again  when  the  blood-stream  is  freed.  Here,  as  in  the 
first  case,  it  makes  no  difference  whether  the  vagi  have  previously 
been  divided  at  the  neck  or  not.  Slow,  rhythmical  compression 
and  release  of  the  aorta — as  best  effected  by  cutting  away  some 
of  the  ribs  on  the  curarised,  artificially  breathing  animal — produce 
similar  rhythmical  variations  of  the  stomach  current.  Every 
protracted  ansemia  of  the  mucosa  retards  the  increase  of  the 
current  very  considerably,  until  finally  recovery  is  no  longer 
possible.  In  dyspnoea  too,  a  marked  negative  swing  always 
follows  upon  the  temporary  increase  of  normal  electrical  action. 
The  simultaneous  tracing  of  the  blood-pressure  on  the  kymograph 
after  double  vagus  section,  proves  that  there  is  no  immediate 
coincidence  between  the  alterations  of  the  arterial  mean  pressure 
in  the  carotid  and  the  variations  of  current,  since  the  negative 
phase  is  usually  developed  at  the  beginning  of  the  dyspnoeic 
increase  of  pressure,  and  continues  after  blood -pressure  has 
returned  to  its  normal  height  by  renewal  of  artificial  respiration. 
The  positive  variation,  on  the  contrary,  occurs  between  the  liegin- 
ning  of  dyspnoea  and  the  first  increase  of  pressure.  It  is 
obvious  that  this  reaction  cannot  be  forthwith  interpreted  in  the 
sense  that  the  progressive  venosity  of  the  blood  caused  the  fall  of 


504  ELECTRO-PHYSIOLOGY 


the  current,  for  when  the  vaso-motor  centre  is  excited,  and  the 
pressure  in  the  aorta  rises,  in  consequence  of  dyspnoea,  the  natural 
concomitant  is  fall  of  pressure  in  the  small  arteries  and  capillaries 
of  many  peripheral  organs,  and  the  stomach  in  particular,  where, 
as  well  as  in  the  viscera,  the  vessels  are  narrowest.  Similar  results 
are  obtained  with  another  experiment  on  the  rabbit,  in  which,  by 
clamping  the  four  arteries  which  supply  the  head,  by  S.  Mayer's 
method  (85),  cerebral  anaemia  is  induced  with  a  consequent 
marked  increase  of  aortic  pressure.  Here,  as  during  dyspnceic 
excitation  of  the  vaso-motor  centres,  the  stomach  current  again 
— after  a  brief  positive  fore-swing — declines  very  markedly,  being 
as  a  rule  already  reversed  at  a  time  wlien  the  hlood-pressure  is  at 
its  maximum.  If  the  clip  is  removed  before  the  centre  has 
become  permanently  injured,  the  blood-pressure  returns  rapidly 
to  its  normal  level,  but  the  current  requires  much  longer  to 
recover  its  original  proportions.  If,  on  the  other  hand,  antemia 
is  prolonged  till  the  blood-pressure  is  at  "  paralytic  "  level,  owing 
to  the  paralysis  of  the  centre,  the  ingoing  direction  of  the  current 
does  indeed  gradually  reassert  itself,  but  never  approximates  to 
its  original  strength,  exhibiting  at  most  a  deflection  of  a  few 
gradations. 

In  view  of  the  last-named  results,  in  which  venous  action  of 
the  blood  passing  into  the  stomach  of  the  slightly  curarised, 
artificially  breathing  animal  seems  to  be  wholly  excluded,  the 
presumption  gains  ground  that  local  decline  of  pressure  in  con- 
sequence of  diminished  arterial  blood-supply  is  in  dyspnoea  also  the 
proper  cause  of  the  negative  variation.  We  should  then  expect 
an  opposite  effect,  i.e.  increase  of  entering  current,  when  pressure 
was  raised  in  the  vascular  system.  One  way  in  which  this  can 
be  accomplished  is  by  transfusion  of  fluids  at  greater  densities. 
It  is  known  from  the  investigations  of  Cohnheim  and  Lichtheim 
(86)  that  even  when  enormous  quantities  of  0'6  °/^  salt  solution 
is  injected  into  the  jugular  vein  of  rabbit  or  dog,  the  blood- 
pressure  undergoes  no  particular  increase,  and  remains  fairly 
normal.  "  There  was  no  question  of  rise  in  ratio  with  the 
densities  injected.  Marked  increase  of  pressure  only  occurred 
during  an  experiment  when  the  initial  pressure  had  been  excess- 
ively low ;  in  this  case  the  infusion  of  fluid  produced  rapid  rise 
of  blood-pressure  to  the  mean."  On  the  other  hand,  a  marked 
axceleration  of  the  circidcdion  was  obvious  in  all  these  experiments, 


V     ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      505 

even  under  the  microscope.  There  was  also  an  extraordinary 
increase  of  bulk  of  water  in  the  blood,  producing  fundamental 
disturbances  of  nutrition  in  the  tissues,  as  exhibited  inter  alia  by 
the  appearance  of  rich  transudations  in  different  organs,  more 
particularly  in  the  abdominal  intestinal  tract.  The  former,  as 
found  by  Cohnheim  and  Lichtheim,  discharged  a  large  bulk  of 
fluid  after  each  plentiful  infusion  of  salt  solution,  while  the 
mucosa  often  swells  to  a  thickness  of  2  cm.,  and  the  intestine 
appears  full  of  exuded  matter. 

A  marked  augmentation  of  the  entering  abdominal  current  is 
nearly  always  exhibited  in  the  rabbit  shortly  after  the  commence- 
ment of  infusion  with  salt  solution,  increasing  more  and  more 
as  the  experiment  progresses,  and  finally  reaching  such  abnormal 
proportions  that  the  galvanometer  mirror  is  driven  off  the  field 
even  when  the  current  has  already  been  compensated.  It  is 
noticeable  that  in  these  cases  a  marked  ingoing  current  may  be 
observed  for  a  long  time  after  the  death  of  the  animal,  which 
never  occurs  under  normal  relations. 

The  significance  of  these,  as  of  the  other  experiments  described, 
can  only  be  indicated  in  a  later  connection.  Here  we  can  only 
state  that  the  fundamental  conformity  in  electromotive  properties 
existing  between  the  mucosa  of  the  frog's  stomach,  and  that  of 
the  tongue,  throat,  and  cloaca,  and  especially  the  fact  that 
all  circumstances  producing  mucous  secretion  tend  to  increase 
the  entering  current,  give  decisive  evidence  that  the  electro- 
motive effects  depend,  if  not  solely,  at  least  in  the  first  degree, 
upon  the  mucin-secreting  elements  of  the  stomach,  i.e.  its  surface 
epithelium.  Whether,  and  how  far,  the  actual  secreting  glands 
are  concerned  in  it,  may  perhaps  be  decided  from  a  more 
detailed  examination  of  the  changes  in  electromotive  action 
which  accompany  the  digestive  processes  in  warm  -  blooded 
animals. 

In  any  case  there  is  not  the  slightest  ground  for  making  the 
peptic  glands  of  the  stomach  alone  responsible  for  the  current 
of  the  mucosa ;  the  less  so,  since  there  is  regularly  a  very  signifi- 
cant quantitative  difference  in  electromotive  action  between  the 
stomach  and  intestine,  which  would  be  unintelligible  if — as 
would  then  be  assumed — the  many  glands  of  the  intestinal 
mucosa  were  as  electrically  active  as  the  glands  of  the  stomach. 
On  the    other   hand,  the  difference   is    easily  understood   if  we 


506  ELECTRO-PHYSIOLOGY 


consider  the  small  number  of  mucin  -  producing  goblet  cells  in 
the  one  case,  and  the  continuous  surface  layer  of  the  same  in 
the  other. 

We  are  of  opinion  that  the  preceding  observations  leave  no 
doubt  that  the  electromotive  effects  described  in  certain  mucosse, 
and  in  the  external  skin  of  naked  amphibians  and  fishes,  are  to  be 
referred  to  the  greater  or  less  number  of  uni-  and  multicellular 
secreting  glands  present,  i.e.,  in  the  last  resort,  to  the  single  cell. 

From  the  standpoint  of  the  earlier  theoretical  account  of 
electromotive  action  it  is  evident  that,  as  regards  the  ex- 
planation  of  the  "  ingoing  current  of  rest,"  no  difficulty  is 
encountered.  Every  goblet  cell,  or  mucous  cell  proper,  ex- 
hibits, as  a  rule,  under  the  microscope  two  clearly  distinguish- 
able sections — one  basal,  nucleated  and  protoplasmic — the  other 
dimmed,  as  a  rule,  by  a  mass  of  granules,  but  on  treatment  with 
reagents  becoming  hyaline  and  turgescent,  i.e.  exhibiting  unmis- 
takable mucin  metamorphosis.  It  must  be  concluded  that 
"  chemical  action  "  in  the  two  parts  of  the  same  cell  differs  not 
only  quantitatively  but  qualitatively  also,  which  explains  the 
difference  of  potential  between  base  and  free  surface,  fundamental 
to  the  ingoing  current,  if  the  mucin  metamorphosis  is  admitted  to 
be  a  chemical  process,  developing  pari  p)cissu  with  the  negative 
potential.  This  naturally  applies  as  much  to  simple,  superficially 
extended  cell  aggregates  (throat  and  cloacal  mucosa,  external  skin 
of  many  fishes)  as  to  the  cases  in  which  there  is  a  more  or  less 
complex  pitting  (glandular  formation) ;  for  it  is  clear  that,  inas- 
much as  these  glands  open  to  the  exterior,  part  of  their  current 
must  be  included  in  the  lead-off,  which  would  naturally  be 
"  ingoing,"  like  the  current  of  the  superficial  mucous  cells.  The 
usually  higher  E.M.F.  of  the  richly  glandular  mucosa  (tongue) 
and  frog's  skin,  vs.  the  fish's  skin,  consisting  only  of  goblet  cells, 
and  the  throat  and  cloacal  mucosa,  may  well  be  referred  to  this 
fact;  for  there  is  no  reason  to  suppose  that  the  sparsely  present 
goblet  cells,  still  less  the  prickle  cells  of  the  frog's  epidermis,  have 
any  such  important  electrical  action.  If,  as  pointed  out  by 
Hermann,  the  form  of  the  glands  in  the  frog's  skin  is  but  little 
suited  to  give  external  galvanic  action,  on  the  other  hand  the 
capillary  layer  of  fluid  which  covers  the  surface  of  the  skin  under 
normal  conditions,  and  must  be  regarded  mainly  as  a  glandular 
secretion,  is  directly  connected  with   the   fluid   contents    of  the 


V     ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      507 

glands,  and  so  makes  a  lead-off  possible.  In  the  tongue,  at  all 
events,  this  is  certainly  the  case.  It  was  said  above  that  the 
other  reasons,  in  particular  the  experiments  of  Bach  and  Oehler 
on  the  corroded  skin,  which  Hermann  brings  forward  against  the 
participation  of  the  glands  in  the  skin  "  rest  current,"  are  by  no 
means  conclvisive.  At  any  rate,  it  cannot  be  denied  that  the 
surface  epithelium  does  contribute  to  the  rest  current  —  the 
more  so,  since  recent  experiments  have  demonstrated  electro- 
motive effects  in  skin  that  is  perfectly  free  of  glands  (88).  If, 
in  view  of  Hermann's  theory  of  the  cause  of  the  entering  skin 
and  mucosa  currents,  it  was  desired  to  predict  the  effect  most 
likely  to  ensue  with  direct  or  indirect  excitation,  the  ^positive 
variation,  i.e.  augmentation  of  the  rest  current,  would  inevitably 
be  selected,  and  explained  by  the  processes  of  alteration  in  the 
glandular  epithelium  strengthened  or  perhaps  initiated  by  excita- 
tion. But  from  the  above  it  appears  that  the  exact  contrary  is 
the  case — the  negative  variation  is  more  and  more  the  exclusive 
consequence  of  excitation,  in  proportion  with  the  E.M.F.  of  the 
entering  rest  current. 

And  that  the  latter  itself  cannot  be  explained  by  the  above 
simple  hypothesis  is  quite  evident  from  the  reactions  described 
with  energetic  cooling.  It  should  here  be  noted  more  especially 
that  in  this  respect  the  complicated,  richly  glandular  objects 
(tongue)  coincide  with  the  most  simply  constructed  (throat  and 
cloacal  mucosa),  so  that  there  can  be  no  question  of  referring  the 
opposite  electrical  effects  before  and  after  cooling,  to  any  anatomi- 
cal difference  in  the  elements.  Hence  no  other  conclusion  is 
possible  but  that  the  same  eioitlulial  cell,  almost  to  the  same  degree, 
is  able  to  give  electromotive  response  noiv  in  the  one  direction  and 
noiu  in  the  other.  In  this,  as  in  many  other  respects,  the  cell 
current  in  question  differs  fundamentally  from  the  electrical 
manifestations  of  nerve  and  muscle.  In  these  the  strongest 
cooling  at  most  produces  diminution,  never,  however,  reversal  of 
the  demarcation  current.  This  is  a  good  instance  of  how  little 
the  galvanometer  is  able  to  indicate  the  quality  of  the  chemical 
process  which  in  both  cases  underlies  the  homodromous  differ- 
ences of  potential.  As  Hering  aptly  remarks,  it  can  only  express 
"  alterations  and  differences  of  chemical  action  in  the  different 
parts  of  a  living  continuum,  together  with  the  magnitude  and 
time  relations  of  such  action." 


508  ELECTRO-PHYSIOLOGY  chap. 

Many  of  these  manifestations,  in  particular  the  frequent  alter- 
nation in  direction  of  the  deflections,  which  appears  spontaneously 
without  any  demonstralDle  cause,  sometimes  also  rhythmically, 
seem  to  indicate  that  each  cell  is  to  he  regarded  as  the  seat  of  tioo 
distinct  chcmiccd  processes,  which — existing  simtdtaneously — "produce 
heteroclromous  potenticds.  The  ohserved  deflection  woidd  therefore 
ahuays  he  the  sum  of  two  antagonistic  forces. 

In  order  to  explain  the  rapid  diminution  and  final  reversal 
of  the  normal  ingoing  current  of  the  skin  and  mucosa  after  cool- 
ing, we  must  assume  that  one  of  the  two  current-generating 
processes  (that  indeed  which  implies  the  development  of  nega- 
tive potential)  is  injured  earlier,  and  to  a  greater  degree,  by 
cold,  than  the  other,  so  that  an  outgoing  current  results  from  the 
preponderance  of  the  latter,  which  in  turn  gives  way  to  an  in- 
going current  so  soon  as  the  normal  conditions  are  restored  by 
heating.  The  "  negative  process  "  appears  to  be  less  resistant  to 
other  effects  also,  than  the  "  positive."  Thus,  as  we  have  seen, 
the  suitable  abstraction  of  water  will  also  revive  the  entering 
current ;  on  the  other  hand,  lack  of  oxygen,  or  treatment  with 
COg,  or  anaisthetising  substances  (alcohol,  ether,  chloroform) 
impair  to  the  same  extent,  and  eventually  abolish,  both  current- 
generating  processes.  In  this  respect  again  the  perfectly  different 
behaviour  of  nerve  and  muscle  currents  should  be  noted,  in 
which  under  these  last  conditions  the  diminution  is  relatively 
late  in  appearing. 

It  is  not  possible  at  this  juncture  to  say  anything  as  to  the 
precise  nature  of  these  chemical  processes  in  the  secretory  cells, 
although  one  is  tempted  to  conjecture  the  secretion  of  water  on 
the  one  hand,  and  organic  specific  secretory  constituents  on  the 
other.  And  in  favour  of  this  view  it  might  be  added,  that  the 
entering  cloacal  current  is  always  strongest  when  the  mucosa  is 
most  richly  covered  with  watery  secretion,  and  that  while  the 
negative  potential  of  the  surface  generally  increases  with  the 
bulk  of  water  present,  it  rapidly  diminishes  with  loss  of  water. 

This  same  interpretation  also  found  unlooked-for  support  in 
the  experiments  described  above  on  the  mammalian  stomach. 

The  extraordinary  influence  of  changes  in  blood-pressure  on 
the  magnitude  of  E.M.F.  in  the  abdominal  mucosa  are  at  any 
rate  to  be  referred  to  this  explanation.  There  can  be  no  doubt 
that  the  secretion  of  water  by  glandular  organs,  apart  from  other 


V      ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      509 

influences,  does  depend  essentially  on  the  actual  pressure,  and  it  is 
at  first  sight  surprising  that  in  the  frog  neither  vagus  excitation, 
nor  complete  abolition  of  circulation,  produces  any  such  effect  on 
the  electromotive  properties  of  the  stomach  as  is  proved  to  be 
the  case  in  mammals,  when  a  relatively  low  fall  of  pressure  in 
the  abdominal  vessels  produces  a  marked  negative  variation  of 
the  ingoing  current.  Yet  this  is  intelligible  in  view  of  the  extra- 
ordinary resistance  of  the  frog's  skin  to  all  injuries  whatsoever. 
Accordingly,  if  decrease  of  pressure  in  the  vessels  of  the  abdominal 
mucosa  is  unfavourable  to  the  secretion  of  water,  a  negative  varia- 
tion must  follow,  if — as  we  are  justified  in  supposing — the  actual 
difference  of  potential  is  the  sum  of  two  antagonistic  electro- 
motive ]3rocesses,  one  of  which  gets  the  upper  hand,  as  soon  as 
any  current  manifests  itself  And  this  appears,  inter  alia,  from 
the  circumstance  that  the  death  of  the  animal  from  any  cause 
whatever,  is  followed  under  normal  conditions  by  a  rapid  decline 
and  subsequent  reversal  of  the  current.  So  that  the  decrease  of 
blood -pressure  in  warm-blooded  animals  seems  to  work  like 
marked  cooling  upon  the  mucous  glands  of  the  cold-blooded,  in- 
asmuch as — if  the  expression  is  legitimate — the  negative  in  both 
cases  declines  more  cjuickly  than  the  opposite  positive  process. 
Erom  this  point  of  view  it  is  easy  to  explain,  not  merely  the 
coincidence  of  result  in  vagus  excitation,  marked  loss  of  blood, 
and  diminished  blood-pressure  due  to  any  poison  (amyl  nitrite, 
pilocarpin,  chloral,  curare,  etc.),  but  also  the  later  effects  of  dysp- 
nceic,  or  ansemic,  excitation  of  the  cerebral  vaso-motor  centres. 

Further  confirmation  of  the  view  thus  laid  down  re  the 
effective  cause  of  the  normal,  ingoing,  abdominal  current,  appears 
from  the  results  of  infusion  of  salt  solution.  Here  the  occasionally 
enormous  secretion  of  water  by  the  mucosa  of  the  stomach 
may  be  directly  observed,  and  when — as  frequently  happens 
— there  is,  notwithstanding  the  pronounced  dilution  of  the 
blood  and  consequent  malnutrition  of  the  tissues,  a  marked 
increase  of  electromotive  action  in  the  mucosa  in  the  sense 
of  the  normal  ingoing  current,  the  only  explanation  possible  in 
the  last  resort  is  that  the  observed  differences  of  potential,  and 
increased  secretion  of  water,  are  in  causative  relation. 

Bayliss  and  Bradford  (87)  previously  came  to  the  same  con- 
clusions with  regard  to  dependence  of  electromotive  action  in  the 
salivary  glands  on  the  nature  of  the  secretion. 


510  ELECTRO-PHYSIOLOGY  chap. 

They  appear  to  have  succeeded  m  the  demonstration  attempted 
hj  Hermann  and  Liichsinger  (79),  of  the  secretion  currents  in 
these  glands.  During  rest  the  surface  of  the  exposed  submaxillary 
gland  of  the  dog  was,  as  a  rule,  negative  to  the  hilus.  The 
E.M.F.  of  this  current  of  rest,  which  must  he  referred,  not 
to  the  injured  region  (muscles),  but  to  the  gland  itself,  varies 
within  a  wide  range  in  different  individuals,  as  also  in  the  same 
animal  at  different  times.  The  altering  relations  within  the 
gland  would  seem  to  be  the  cause  of  this — as  is  attested  by  the 
fact  that  permanent  changes  of  the  current  of  rest  are  induced 
not  merely  by  temporary  excitation  of  the  gland  nerves,  but 
also  by  atropin  poisoning.  The  direction  of  the  rest  current 
varies  much  more  (being  indeed  frequently  reversed)  in  the  sub- 
maxillary of  the  cat  than  in  the  dog  (surface  positive  to  hilus). 
This  is  the  more  striking,  in  view  of  the  extensive  morphological 
coincidence  of  this  gland  in  the  two  animals,  since  the  rest 
current  of  the  "  serous  "  parotid  gland  in  the  dog  generally  agrees 
in  direction  with  that  of  its  submaxillary. 

Hence  it  would  appear  that  functional  differences  in  the 
glands  regulate  the  observed  differences  of  potential.  The 
behaviour  of  the  "  action  current "  on  exciting  the  secretory 
nerve  also  speaks  for  the  same  conclusion.  After  compensating 
the  current  of  rest,  excitation  of  the  chorda  tympani  in  the  dog 
always  causes  negativity  of  the  external  surface  of  the  sub- 
maxillary gland.  The  period  of  this  variation  is  often  interrupted 
by  a  second  antagonistic  phase,  which  sometimes  expresses  itself 
only  in  a  retardation  or  temporary  stand-still  of  the  deflection, 
while  it  is  frequently  masked  altogether  by  the  first  and  more 
pronounced  principal  phase.  The  deflection  begins  after  a  short 
latent  period,  before  any  secretion  has  appeared  in  the  canal,  and 
where  the  excitation  is  weak  it  forms  the  only  manifestation. 

Excitation  of  the  cervical  sympathetic  also  invariably  pro- 
duces electromotive  action  in  the  submaxillary  glands  of  the 
dog,  distinguished,  however,  from  the  above  by  smaller  effect, 
longer  latent  period,  and  monophasic  variation  (surface  positive 
to  hilus),  i.e.  the  reverse  of  the  principal  phase  in  chorda 
excitation. 

In  the  same  gland  of  the  cat,  on  the  contrary,  the  second 
phase  (surface  positive  to  hilum)  is  the  more  pronounced  with 
excitation  from  the  chorda.      Bayliss  and  Bradford  find   immis- 


V     ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS      511 

takable  relations  between  the  strength  of  both  phases  and  the 
nature  of  the  glandular  secretion,  since  it  regularly  appears  that 
the  first  phase  predominates,  or  even  appears  exclusively,  where 
the  secretion  is  plentiful  and  watery,  the  second  when  it  is 
sparse,  but  rich  in  mucin.  The  observed  differences  in  electrical 
action  of  the  submaxillary  in  cat  and  dog  respectively  would 
thus  be  explained  by  the  actual  diversity  in  the  secretion  yielded 
in  either  case  on  chorda  excitation,  since  in  the  dog  it  is  much 
more  watery  than  in  the  cat. 

While  in  the  dog,  excitation  of  the  sympathetic  only  produces 
an  extremely  viscid  and  scanty  secretion,  in  the  cat,  on  the  other 
hand,  it  is  plentiful  and  watery.  The  electrical  effects  are 
correspondingly  small,  with  prevailing  second  phase,  in  the  first 
case — in  the  second  they  are  considerable,  and  even  exceed  the 
effect  of  chorda  excitation.  Bayliss  and  Bradford  consider  that 
poisoning  with  atropin  excludes  the  action  of  simultaneous, 
vaso- motor  effects  in  the  electromotive  effects  observed,  since 
while  this  drug  has  no  vascular  action,  it  soon  abolishes,  or  very 
strongly  affects,  secretory  and  electrical  functions. 

Another  observation  of  the  same  authors  on  the  submaxillary 
and  parotid  of  the  dog  must  also  be  noticed.  Excitation  of  the 
sympathetic,  as  a  rule,  produces  no  quantity  of  secretion 
from  the  last  -  named  gland,  yielding  only  a  few  drops  of 
viscid  submaxillary  saliva.  Under  certain  conditions,  however, 
especially  after  repeated  excitation  of  the  cerebral  gland  nerves, 
a  more  plentiful  secretion  appears,  with  corresponding  alteration 
of  electromotive  action.  While  the  surface  of  both  glands  is 
usually  positive  to  the  hilus  in  excitation  from  the  sympathetic, 
in  this  instance  an  opposite  variation  appears  (when  the  cerebral 
gland  nerves  are  excited),  either  alone,  or  as  an  accentuated 
preliminary  phase.  Bradford  is  inclined  to  bring  the  first 
electrical  change  (second  phase)  into  causative  relation  with  the 
formation  of  the  organic  constituents  of  the  saliva,  while  he  refers 
the  opposed,  usually  stronger,  variation  to  the  processes  of 
secretion  of  water. 

If  the  views  thus  set  forth  are  legitimate,  we  should  naturally 
regard  both  entering  and  outgoing  currents  of  the  glands  as 
"secretion  currents,"  i.e.  the  galvanic  expression  of  permanent 
chemical  action  in  the  secretory  cells,  and  there  would  be  no 
question  of  the  appearance  of  a  new  electromotive  force  derived 


512  ELECTRO-PHYSIOLOGY 


from  another  source,  or  other  elements,  in  consequence  of 
excitation,  but  solely  of  alteration  in  the  galvanic  effects  of  the 
same  elements,  which  must  be  regarded  during  rest  as  the  cause 
of  the  differences  in  potential. 

From  this  point  of  view,  explanation  of  the  actual  experi- 
mental effects  consequent  on  excitation,  presents  no  serious 
difficulties,  even  when  complicated  double,  or  multiple,  variations 
are  exhibited.  Taking  first  the  simple  case,  where,  as  in  the 
frog's  tongue,  a  strong  ingoing  current  is  present  from  the  be- 
ginning, augmentation  of  the  same,  i.e.  a  2^ositive  variation,  is 
only  likely  to  appear  when  (with  direct  or  indirect  excitation) 
the  "negative  process"  is  increased  above  the  "positive,"  which  in  the 
instance  cited,  where  that  is  already  so  preponderant,  is  not  very 
probable ;  it  seems  much  more  likely  that  the  process  which  is 
initially  less  developed  should  be  increased  by  excitation  than 
the  other.  From  this  standpoint  it  would  also  be  comprehensible 
that  a  "  negative  variation  "  should  follow  upon  excitation,  the 
more  exclusively  and  distinctly  in  proportion  as  the  original 
current  is  stronger.  That,  further,  a  positive  after-effect  fre- 
quently makes  its  appearance,  is  also  intelligible,  as  soon  as 
it  is  realised  (as  proved  by  experiment)  that  the  positive 
effect  which  depends  on  augmentation  of  the  "  negative  process  " 
invariably  declines  much  more  slowly  than  the  opposite  effect, 
so  that  when  the  one  has  already  returned  to  its  normal,  the 
other,  from  its  greater  constancy,  entails  a  positive  increment  of 
the  original  current. 

The  conditions  of  appearance  of  a  positive  variation  during 
excitation,  either  independently  or  as  fore-swing  to  a  subsequent 
negative  variation,  are  accordingly  so  much  the  more  favourable 
in  proportion  as  the  homodromous,  incoming  current  is  weaker, 
i.e.  as  the  "  negative  process  "  is  less  preponderant.  For  obviously 
there  is  then  greater  opportunity  of  strengthening  this  latter 
so  much  by  excitation  that  it  in  turn  becomes  uppermost. 
Strength  of  the  tetanising  current  is  also  an  important  factor, 
since  it  would  appear  that  the  process  leading  to  development  of 
negative  potential  at  the  surface  is,  under  equal  conditions,  more 
easily  excited  than  its  opposite,  so  that,  as  more  especially  in  the 
mucosa  of  throat  and  cloaca,  the  positive  effect  appears  with 
weak,  the  diphasic  or  single  negative  effect  with  stronger,  excita- 
tion.    In  particular  cases  a  diphasic  effect  may  of  course  appear 


V      ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  C4LAND  CELLS      513 

with  many  variations,  as  regards  the  succession  of  the  two 
pliases.  While  in  the  cloaca  with  a  moderately  strong  entering 
mucosa  current,  a  positive  variation  usually  precedes  the  stronger 
negative  effect  as  a  fore-swing,  in  the  mucosa  of  the  throat,  under 
the  same  conditions,  the  negative  is  very  frequently  interrupted 
by  a  positive  swing.  It  is  clear  that  even  with  complete  equality 
of  the  two  current -generating  processes  (when  currents  that 
can  he  led  off  externally  are  altogether  wanting)  the  possibility 
of  a  "  secretion  current "  is  not  excluded,  provided  the  one  or 
other  process  is  preponderant.  Since,  in  view  of  the  experimental 
reactions  under  discussion,  this  is  rather  to  be  expected  of  the 
"  negative  "  than  of  the  "  positive  "  process,  it  is  intelligible  that 
positive  deflections  in  the  direction  of  an  ingoing  current  should  be 
visible  where  the  excitation  is  not  too  strong.  More  frequently, 
however,  all  galvanic  effects  of  excitation  are  wanting,  from 
which  it  must  not,  of  course,  be  concluded  that  the  secretory 
process  excited  by  the  current  is  absent,  but  merely  that  a 
particular,  physical  symptom  of  the  same  has  in  this  case  not 
found  expression.  While,  finally,  it  seems  almost  self-evident — 
from  the  previous  argument — that  where  there  is  a  "  reversed  " 
outgoing  current  in  consequence  of  excitation,  there  should  also 
be,  in  an  overwhelming  majority  of  cases,  deflections  of  the 
magnet  in  the  direction  of  an  ingoing  current.  At  all  events 
this  is  the  case  almost  without  exception  with  weaker  excitation, 
while  stronger  stimuli,  even  under  these  conditions,  may  still 
produce  a  positive  variation. 

The  electromotive  action  of  the  skin  glands  (sweat  glands)  of 
mammals  and  of  man  is  far  less  exactly  determined  than  in  the 
uni-  and  multicellular  mucous  glands.  Ever  since  du  Bois-Eey- 
niond  exhibited  his  famous  experiment  (at  first  referred  to  the 
action  current  of  the  muscles)  on  man,  in  which  the  lead-off  is 
from  both  hands  or  both  feet,  symmetrically,  after  which  voluntary 
contraction  of  one  arm,  or  one  leg,  deflects  the  magnet  of  the 
multiplier,  it  was  conjectured  that  this  might  indicate  the 
development  of  an  entering  skin  current  in  consequence  of 
excitation.  After  Hermann's  observations  it  must  be  admitted 
that  the  action  current  from  the  muscles  plays  no  part  in  it, 
while  if  any  doubt  could  still  remain  on  this  point,  it  must  finally 
give  way  before  the  experiments  of  Hermann  and  Luchsinger  on 
the  secretory  currents  of  the  cat's  skin.      As   we  pointed  out  in 

2  L 


514  ELECTRO-PHYSIOLOGY  chap. 

an  earlier  connection,  du  Bois-Eeymond's  experiment  concerns 
not  the  presence  of  the  secretion,  but  the  secretory  process,  where 
the  visible  appearance  of  sweat  is  not  required. 

The  same  applies  in  every  detail  to  the  pad  of  the  cat's  foot, 
which  is  rich  in  sweat-glands.  Symmetrical  leading-off  from  the 
two  plantar  balls  gives,  normally,  no  current  of  importance,  but 
current  is  at  once  produced  when  the  sciatic  nerve  is  cut  through 
on  one  side.  This  current  is  always  directed,  in  the  animal, 
from  normal  to  paralysed  side  (ingoing).  After  dividing  the 
second  sciatic  the  difference  of  potential  disappears  entirely,  to 
reappear  if  one  or  other  nerve  is  artificially  excited  after  curarisa- 
tion.  That  this  really  is  a  secretion  current  is  proved  by  the 
action  of  atropin — the  latency  of  the  galvanic  effect  is  in  the  first 
place  perceptibly  increased,  and  the  intensity  of  the  current  declines, 
and  is  quickly  abolished.  On  leading  off  from  the  undisturbed 
surface  of  the  exposed  muscles  and  the  uninjured  epidermis,  the 
incoming  current  of  rest  appears  to  sink  on  removal  of  the 
epithelial  layer.  "  When  pilocarpin  is  injected  into  one  foot, 
and  the  lead-off  is  symmetrical  from  both  feet,  there  is  invariably 
a  strong  current  from  the  injected  side  to  the  other,  i.e.  increase 
of  entering  skin  current."  Excitation  of  the  central  end  of  the 
sciatic  produces  a  reflex  current  from  the  unexcited  to  the  excited 
side,  where  the  glands  are  separated  by  the  division  of  the  nerve 
from  the  central  organ.  The  same  effect  occurs  with  central 
excitation  of  the  cruralis  (Hermann).  The  experiment  of  lead- 
ing off  symmetrically  from  one  paralysed  and  one  non-paralysed 
foot  of  a  cat  sweating  freely,  either  by  reason  of  its  struggling, 
or  in  the  warm  chamber,  is  obviously  complementary  to  du  Bois' 
experiment  on  man ;  there  cannot  be  the  slightest  doubt  of  its 
significance,  since  the  current  persists  under  the  application  of 
curare,  notwithstanding  abolition  of  muscular  contraction,  while 
atropin  on  the  other  hand  neutralises  the  difference  of  potential 
although  muscular  contraction  continues. 

An  unmistakable  secretion,  which  is  demonstrably  under 
nerve-control,  is  also  evident  on  the  skin  of  the  upper  lip  and 
nose  of  the  calf,  as  well  as  the  nostril  of  sheep  and  goat.  It 
derives  apparently  from  the  large,  acinous  glands  which  are 
seated  there.  Excitation  of  the  vago-sympathetic  always  pro- 
duces increased  secretion.  So  too  in  the  hairless  snout  of  the 
pig,   in    which   excitation    of    the    peripheral    (cephalic)    end   of 


V     ELECTROMOTIVE  ACTION  OF  EPITHELIAL  AND  GLAND  CELLS     515 

the  divided  sympathetic  discharges  large  drops  of  secretion 
from  the  openings  of  the  snout  glands  on  the  same  side.  Sym- 
metrical leading-off  from  two  points  of  the  surface  then  gives  a 
strong  ingoing  secretion  current,  with  an  E.M.F.  of  possibly  0'07 
Dan.  The  difference  of  potential  in  the  nose  of  the  goat,  and 
still  more,  dog  or  cat,  is  much  less,  owing  in  the  last  case  to 
the  comparative  scantiness  of  the  secretion. 


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2  L  2 


INDEX 


Absence  of  current  in  uninjured  muscle, 

•341 
Abstraction    of   water,    action    on   muscle, 

429  ;  on  the  skin,  472,  479 
Actinosphferium,  electrical  excitation,  299 
Action  current  of  muscle,  359  ff. ;  in  man, 
391  ;   on  the  heart,  396  ;.  methods  of 
investigation,    362,    399,    408,    410  ; 
phasic    and   decremental,    3S1  ;    with 
indirect      excitation,     384  ;      theory, 
374 
Addition  latente,  117 

Adductor  muscle,  of  mollusca,  68  ;  touus, 
100  ;    contraction,     178,     187,     190  ; 
polar   excitation,    222  ;    electromotive 
action,   345  ;  secondary  electromotive 
manifestations,  455 
After-effects  of  galvanic  current  in  muscle, 
443  ;    excitatorj^,   see  opening  excita- 
tion ;   inhibitory,  258   ff. ;   alterations 
of  excitability  from,  287,  292 
After-loading  of  muscle,  121  ff. 
Alkalis,  action  on  muscle,  104,  221 
Alteration  theory,  Hermann,  351 
Ammonia,  action  on  secondary  excitation  ; 

from  muscle  to  nerve,  413 
AmoebEe,  electrical  excitation,  305 
Anabolic  (katabolic)  nerves,  433 
Ansesthesia,    effect    on    electromotivity    of 

muscle,  358,  450 
Anelectrotonus.     See  electrotonus 
Anode,    physiological,     212  ;    relation    to 
break    excitation,     214  ;      inhibitory 
action,  236,  257,  264  ;   anodic  closure 
excitation  of  protozoa,    305  ;    excita- 
bility, 289  ;  anodic  (positive)  polarisa- 
tion in  muscle  and  nerve,  445 
Anodonta,    adductor    muscle,    68  ;    tonus, 

100  ;  electrical  excitation,  187,  233 
Apex-time,  and  height  of  apex,  115 

Bat,  muscle-fibres,  32  ;  distribution  of 
twitch,  63 

Beetle,  structure  of  muscle,  34  ;  contrac- 
tion wave,  63 


Capillary  electrometer,  401 

Cell  conduction  in  smooth  muscle,  169 

Cell  currents,  theory,  508 

Cephalopoda,  muscle-cells,  15 

Closure  contraction  (persistent),  183,  205 

Closure  tetanus,  secondary  inefficacy,  422 

Cnidarians,  epithelial  muscles,  10,  11 

Cohnheim's  Arese  in  muscle,  29 

Cold,  action  on  muscle,  97  ;  on  muscle 
current,  338 

Compensator,  round,  336 

Conductivity,  in  muscle,  144  ff.  ;  in  the 
heart,  162;  in  smooth  muscular  organs, 
165  ;  electrotonic  alterations  in  muscle, 
295  ;  of  excitatory  wave,  373,  in  the 
heart,  397 

Constant  current,  action  on  muscle,  174  : 
on  protozoa,  301 

Contractility,  3 

Contraction,  alteration  in  optical  properties 
of  muscle,  49  ;  rhythmical  on  excitation 
with  the  constant  current,  195  ;  rhyth- 
mical with  chemical  excitation,  106 

Contraction  wave,  variations  in  rapidity, 
151  ;  length,  168 

Contracture,  89 

Core-model,  448 

Cross-striation  of  muscle,  40  ;  in  state  of 
contraction,  48 

Current  intensity,  effect  on  height  of 
twitch,  69 

Current  distribution,  346 

Current  oscillation,  excitatory  action  on 
muscle,  176,  286 

Death  of  muscle,  90  ;  effect  on  conductivity, 
151,  on  excitability,  182,  343  ;  rela- 
tion to  muscle  current,  337,  343,  352  ; 
to  current  of  action,  382,  388 

Death,  local,  effect  on  polar  excitation  by 
current,  218 

Decline  (internal)  of  muscle  current,  332 

Decrement  of  contraction  wave  in  muscle, 
149  ;  absence  in  living  human  subject, 
395 


620 


ELECTRO-PHYSIOLOGY 


Demarcation  current,  321 
Demarcation  surface,  337,  352 
Dissimilation   (and   assimilation)   of  living 

matter,  83 
Double  myograph,  175 
Double  refraction  of  mnscle,  46 
Duration  of  current,  excitatory  action,  178 

Echinus,  electrical  excitation  of  muscles, 
238 

Electricity,  action  on  muscle,  174  ff. ;  on 
protozoa,  299  ff.  ;  resistance  of  muscle, 
200;  "general  law"  of  excitation, 
191  ;  influence  of  direction  of  current, 
199,  of  density,  209,  216 

Electrodes,  unpolarisable  for  muscle,  174 

Electromotive  force,  measurement,  335 

Electrotonus,  polar  alterations  of  excit- 
ability iu  muscle,  280 

Epithelial  muscles,  10 

Ether,  effect  on  muscle  current,  359  ;  on 
action  current,  450 ;  on  gland  cur- 
rents, 473 

Excitability,  direct  in  muscle,  69  ff.  ;  of 
different  muscles,  57  ff.  ;  nature  at 
death,  91  ;  effect  of  circulation,  95  ; 
of  temperature,  97  ;  of  fatigue,  83  ff. ; 
of  the  galvanic  current,  276  ff. ;  of 
transverse  section,  227  ;  of  desiccation, 
429  ;  of  glycerin,  432  ;  of  chemical 
substances,  104 

Excitation  of  muscle  by  its  own  current, 
326  ;  secondary,  muscle  to  muscle, 
427 

Excitatory  wave,  in  muscle,  373  ;  relation 
to  contraction  wave,  376 

Fall  rheotome,  353,  385 

Fatigue  in  muscle,  83  ;  local,  by  current, 

223 
Flagellata,  electrical  excitation,  307,  308 
Freezing  of  muscle,  103 
Frog's  skin,  electromotive  action,  462  ff. 

Galvanic  current.     See  constant  current 
Galvanic    resistance    to    conductivity    in 

muscle,  200 
Galvanotropism  iu  protozoa,  307 
Gastrocnemius  muscle,  electromotive  action, 

325 
Glands,  electromotive  action,  461  ff. 
Glycerin,  action  on  muscle,  432 
Goblet  cells,  electromotive  action,  474 
Granules,  interstitial,  in  muscle,  30,  33 

Heart,  contraction  wave,  163  ;  excitatory 
wave,  399  ;  absence  of  current  in 
iminjured  state,  343  ;  positive  varia- 
tion of  demarcation  current  in  vagus 
excitation,  434  ;  nature  of  demarca- 
tion current    344  ;    secondary  twitch 


from  heart,  396,  420,  427  ;  current  of 
action,     397  ;    structure    of    muscle- 

,  fibres,  24,  91  ;  contraction  curve, 
56  ;  strength  of  stimulus,  70  ;  effect 
of  tension,  79  ;  electrical  excitation, 
194,  257 

Heat,  93,  339 

Hippocampus  float-muscles,  structure,  30 

Holothuria  muscles,  electrical  excitation, 
234 

Hydra,  neuro -muscular  cells,  9 

Idio-muscular  contraction,  152,  172,  205, 
225,  390 

Inclination  current,  325 

Induction  currents,  action  on  muscle,  119, 
179,  181,  218  ;  on  protozoa,  299,  305 

Inhibitory  manifestations,  anodic  in  muscle, 
243  ;  in  intestine,  247 ;  in  the  heart, 
257  ;  in  striated  muscle,  267 

Initial  twitch,  133,  315  ;  cardiac,  134 

Innervation,  voluntary,  138  ff. 

Insect  muscles,  structure,  33  ff.  ;  contrac- 
tion phenomena,  49  ;  distribution  of 
twitch,  64;  tetanus,  125, 132  ;  fatigue, 
91  ;  propagation  of  contraction,  155, 
164 

Interference  of  excitation  between  excita- 
tory and  muscle  currents,  329 

Intersections,  tendinous,  228 

Intestine,  electrical  excitation,  240,  248  ff. 

Katabolic  nerves,  433 
Katelectrotonus.     See  electrotonus 
Kathode,  inhibition  of  condiictivity,  295  ; 

excitability,  280,   287  ;  physiological, 

212 
Kiihne's  bifurcate  experiment,  430 

Latent  period,  56  ;  of  negative  variation, 
375  ;  of  muscle  elements,  73  ;  depend- 
ence on  strength  of  excitation,  72  ;  of 
opening  excitation  in  muscle,  190  ; 
dependence  on  current  density,  216 

Leech,  electrical  excitation  of  cutaneous 
muscular  integument,  245 ;  electro- 
motive action  of  skin,  477 

Man,  phasic  action  current  in,  394  ;  skin 

current,   393,   513  ;  action  current  of 

heart,  405 
Microphone,  133 
Molecular   theory,    electrical,    of    muscle, 

347 
Molecules,  i^eripolar,  348 
Mollusca,  adductor  muscle,   68,   100,   177, 

187,  233 
Mucosa  currents,  464  ff. 
Mucosa,    electromotive    action    in   tongue, 

464  fr.  ;  throat  and  cloaca,    473  ff.  ; 

stomach,  500  ff. 


INDEX 


521 


Muscle,  smooth,  21,  92  ;  striated,  3  ; 
quick  and  sluggish,  57  ff.,  65  ;  red 
and  pale,  60  ;  contraction,  48,  54  ; 
microscopic  reaction,  46  ;  distribution 
in  time,  56  ;  natural  muscular  con- 
traction, 139  ;  propagation  of  con- 
traction wave,  146  ff .  ;  polymerous 
muscle,  228 

Muscle  columns,  20,  25,  32 

Muscle  current,  resting,  321  if.,  334  ;  weak 
longitudinal  current,  322;  E.M.F., 
335  ;  decline,  343,  344  ;  in  uninjured 
muscle,  345  ;  negative  variation,  362  ; 
positive  variation,  368  ff.  ;  excitation 
from  muscle,  326,  362,  427  ;  inclina- 
tion current,  325  ;  law  of,  353 

Muscle  tone,  135-139 

Muscular  tonus,  100,  235,  260,  265 

Myogra,m,  57 

Myograph,  56 

Myonema  of  infusoria,  4 

Negative  variation,  of  muscle  current, 
362,  370  ;  in  the  heart,  396  ;  theory, 
388  ;  of  skin  current,  481  ff.  ;  in 
excitation  of  secretory  nerves,  486, 
500 


Oblique  striation,  in  muscle,  15  ff. 
Opening  contraction  (persistent),  186,  210, 

233 
Opening  inhibition,  anodic  and  kathodic  in 

the  heart,  263 
Opening  twitch,  spurious  in  excitation  of 

muscle,  329,  334 

Pakam^ecium,     galvanotropci     manifesta- 
tions, 308  '-^ 
Parelectionomy,  338  ft'. 
Pelomyxa,  electrical  excitation,  305 
Photogram  of  action  current,  402  fl'. 
Polar  action  of  electrical  current  on  muscle, 
203,  216  ;  on  the  heart,  228  ff.,  258  ; 
on  protozoa,  302  ;  on  ova,  310 
Polarisation,  galvanic,  of  muscle,  279  ;  mor- 
phological, of  ova,  310  ;  internal,  442  ; 
positive  of  muscle,  443 
Pole,  definition  of  physiological,  212 
Polystomella,  electrical  excitation,  303 
Porret's  phenomenon  in  muscle,  273 
Potassium  salts,  action  on  muscle,  67,  172  ; 
on  polar  excitation,  220  ;  on  electro- 
motive action,  355,  356 
Pre-existence  of  miiscle  current,  338 
Pressure  of  muscle,    action    on    secondary 
excitation  from  muscle  to  muscle,  427 
Protozoa,  electrical  excitation,  299 
Pseudopodia,  reaction  in  electrical  excita- 
tion, 300 


Rapidity   of    excitation    and    contraction 

wave  in  muscle,  147,  374 
Reaction  of  degeneration,  182,  273 
Refractory  period,  in  the  heart,  288 
Renewal  of  cross-section,  effect  on  muscle 

current,  344 
Resistance  to  conductivity  in  muscle,  200 
Rheotachygraphy,  373,  386 
Rheotome,    Bernstein's    differential,    367  ; 

fall,  353,  385 
Rhizopoda,  electrical  excitation,  299 

Salivary     glands,    electromotive     action, 

509,  510 
Salpa  muscles,  20 

Salt  (common),  action  on  muscle,  104 
Sarcoplasm,  28  ff.,  68,  90 
Secondary  electrode  points,  effect  on  polar 

excitation,  255 
Secondary  electromotive  manifestations  in 

muscle,  442  ft'. 
Secondary  excitation,  from  muscle  to  nerve. 

361,     396,     413  ;     from    muscle     to 

muscle,  427 
Secretion  currents,  463,  485,  513  ;  in  man, 

393,  395 
Skin  current,    in   frog,    462  ff.  :    in    man, 

391 
Sodium  salts,  action  on  muscle,  105,  221 
Staircase  contraction,  71,  121,  123 
Strength  of  current,  as  affecting  height  of 

twitch,  70 
Summation  of  stimuli,  1 1 3  ff. 
Superposition  of  twitches,  115 
Supported  muscle,  effect  on  twitch,  121 
Survival  of  smooth  muscle,  92 

Telephone  as  rheoscope,  410,  424 

Temperature,  effect  on  muscle,  91,  97  ft"., 
151  ;  on  muscle  current,  339 ;  on 
gland  currents,  468 

Tension,  effect  on  muscle  twitch,  76  ff. 

Tetanus,  nature  of,  113  ff.;  rhythmical,  131, 
135;  natural,  139;  strychnia  tetanus, 
143  ;  in  muscles  that  are  functionally 
dissimilar,  125  ;  in  heart,  129;  gal- 
vanic manifestations,  364  ;  secondary 
from  muscle,  364 

Tonus  in  smooth  muscle,  100  ;  in  cardiac 
muscle,  102 

Tortoise  muscles,  61,  124 

Transverse  passage  of  current  in  muscle, 
199 

Transverse  resistance  of  muscle,  200 

Transverse  section,  artificial,  relation  to 
muscle  current,  322  ;  effect  on  polar 
excitation  by  current,  21 7  ;  on  opening 
excitation,  330 

Twitch,  secondary  from  muscle,  effect 
of  tension  in  primary  muscle,  413  ; 
with     direct    excitation    of    primary 


522 


ELECTRO-PHYSIOLOGY 


muscle,  416  ;  position  of  secondary 
nerve,  417  ;  summation  of  stimuli, 
421  ;  discharged  by  closing  and  open- 
ing tetanus,  422,  and  vital  tetanus, 
422 ;  isotonic  and  isometric,  82 

Under-propping,  eifect  on  twitch,  121 

Vagus,  action  on  the  heart,  433 
Veratriu,  action  on  striated   muscle,    107, 
265 


Voltaic  alternative,  in  muscle,  224,  292 
Vorticella,  stalk  muscle,  4 


Water  rigor,  357 

Wave  of  contraction,  151  ff.,  168  ;  of  excita- 
tion, 373  ;  relation  to  contraction 
wave,  376 

Worms,  muscles,  12  ;  electrical  excitation 
of  cutaneous  muscular  integument, 
240  tf. 


THE  END 


Printed  by yi^.  &  R.  Clark,  Limited,  Edmburgh 


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